How to Issue Foreign Language Invoices in KSeF?

If you run a sole proprietorship (JDG) in Poland and Polish isn't your first language, using invoicing software in English in Poland, or in Ukrainian, is completely legal. Polish VAT law does not set a language for invoices between businesses. Three things matter: correct data in KSeF, the VAT amount in Polish złoty, and a Polish version of your documents when the tax office asks for it or when you sell to consumers.

I'm writing this as a developer who builds a KSeF integration and as a foreigner running a business in Poland myself. Below I explain where language matters, where it doesn't, and how to choose a tool that won't leave you stuck during a tax audit.

Can an invoice in Poland be in English or Ukrainian?

Yes, in business-to-business trade. Neither the VAT Act, nor the regulations issued under it, nor the Tax Ordinance specifies the language of an invoice. The Ministry of Finance confirmed this position years ago (source: Infor, "500 questions about VAT").

There are three rules to keep in mind:

1. Consumers in Poland. The Polish Language Act (Art. 7) requires Polish in transactions with consumers. If you invoice a private person, issue the document in Polish or bilingually.

2. VAT always in PLN. Even if the invoice is in euro and in English, the tax amount must be converted to złoty (Art. 106e(11) of the VAT Act).

3. Translation on request. During a tax audit you must provide a Polish translation of documents prepared in a foreign language (Art. 287 §1 point 2 of the Tax Ordinance). The law does not say explicitly whether it has to be a sworn translation.

In practice, the safest option is a bilingual invoice: Polish plus your client's language. You and your client understand the document, and the tax officer doesn't have to wait for a translation.

Three layers of language: interface, KSeF XML and visualisation

Since KSeF went live, the word "invoice" means something different. Technically you deal with three separate layers, and each has its own language rules.

1. The software interface

This is the language of menus, buttons and error messages. The law doesn't regulate it, because the interface is not a document. If "Issue invoice" is clearer to you than "Wystaw fakturę", you can work in English or Ukrainian and still send exactly the same document to KSeF as someone using the Polish version.

This matters more than it seems. Most invoice errors don't come from the law itself but from misreading a form field, for example confusing the sale date with the issue date or choosing the wrong VAT rate.

2. The XML file in KSeF (FA(3) schema)

A structured invoice is an XML file that follows the FA(3) schema. Element names are Polish and fixed (e.g. Podmiot1 for the seller), so they can't be "translated". The content of the fields, such as the service description, can be in a foreign language. The Ministry of Finance explicitly allows foreign-language data in the XML file (quoted by ifirma.pl).

One note from the developer side: KSeF XML is UTF-8, so technically it will accept Cyrillic too. But the same file is later read by your Polish buyer and their accountant. A description in Polish or English is simply more practical.

3. The visualisation (PDF for the client)

When a client doesn't receive the invoice through KSeF, for example a company abroad, you send them a visualisation, usually a PDF. The Ministry doesn't impose a template and allows the visualisation to be in a foreign language or bilingual, as long as it matches the XML file in substance. An invoice used outside KSeF must carry a QR code and the KSeF number.

This isn't a formality. In 2026 rulings, the Director of the National Tax Information (KIS) indicated that a visualisation that differs from the document in KSeF may be treated as a separate invoice (source: Gazeta Prawna). That's why the PDF should be generated automatically from the same data as the XML, not retyped in a text editor.

KSeF for foreigners: deadlines, login and penalties

Your citizenship doesn't matter here. What counts is your VAT status and your Polish NIP (tax number).

Date What changes (as of October 2026) 1 February 2026 Issuing obligation for the largest companies; all VAT payers must receive invoices via KSeF 1 April 2026 Issuing obligation for all other businesses, including most JDGs 1 January 2027 Smallest taxpayers (invoiced sales up to PLN 10,000 gross per month), penalties start, KSeF number required in bank transfers

Penalties. From 1 January 2027 the head of the tax office may impose a penalty of up to 100% of the VAT shown on an invoice issued outside KSeF, or up to 18.7% of the total amount due for an invoice without VAT (Art. 106ni of the VAT Act). The penalty is scaled to the seriousness of the breach. No administrative penalties are imposed in 2026.

Login. You can authenticate in KSeF with, among others, a Trusted Profile (Profil Zaufany), a qualified electronic signature or a KSeF certificate. A Trusted Profile requires a PESEL number, so if you don't have one, check early which method you'll use. KSeF tokens only work until 31 December 2026. From 2027 you need KSeF certificates or a permission granted to your invoicing software.

A note for non-Polish speakers: the Ministry's free tools (the KSeF Taxpayer Application and the mobile app) are designed primarily in Polish. In 2026 consultations with the Ministry, experts listed an English version of the platform among the most needed changes (source: podatki.biz). That's why invoicing software in Ukrainian or English is real help for many people, not just a convenience.

How to choose invoicing software in English or Ukrainian

Separate two things that offers often mix up: the interface language (what you work in) and the document language (what your client receives). Software can have a Polish menu and issue invoices in English, or the other way round.

Criterion Why it matters Interface in your language Fewer mistakes when filling in fields Bilingual invoices (PL + EN/UA) Your client understands the document, and so does the tax office Direct KSeF integration with UPO An invoice legally exists only once it has a KSeF number Visualisation generated from XML, with QR code PDF stays consistent with KSeF, no "second invoice" risk Foreign currencies with NBP rate VAT converted to PLN automatically Receiving purchase invoices from KSeF Mandatory for every VAT payer since 1 February 2026 JPK_V7, records and ZUS in one place Less copying of data between tools

Several tools on the Polish market support other languages. A few examples based on vendor information (as of 8 October 2026):

• Fakturownia offers an interface in, among others, English and Ukrainian, plus bilingual invoices (fakturownia.pl/po-ukrainsku).

• wFirma lets you issue invoices in nine language versions, including English and Ukrainian, with Polish and foreign-language labels (pomoc.wfirma.pl).

Before you decide, open a test account and check one thing: issue an invoice in euro for a foreign client and see whether the PDF includes the KSeF number, the QR code and the VAT amount in złoty.

Common invoicing mistakes foreigners make

• English-only invoice for a private person in Poland. A consumer should get a Polish or bilingual document.

• A PDF from Word instead of a KSeF invoice. If KSeF applies to you, a PDF alone is not an invoice. From 2027 this can trigger a penalty under Art. 106ni.

• No KSeF invoice for a foreign client. An invoice for a foreign company also goes to KSeF; the client gets a visualisation with a QR code.

• Editing the PDF after sending to KSeF. Any difference between PDF and XML is a risk. Mistakes are fixed with a corrective invoice.

• Postponing the change of login method. KSeF tokens expire on 31 December 2026.

How we approach this at Biurko

We build Biurko from the perspective of a developer who runs a JDG in Poland as a foreigner himself, which is why the interface is available in Polish, English and Ukrainian. You issue and receive invoices in KSeF (FA(3)) with UPO confirmation, and the connection works through a permission you can revoke at any time in the KSeF portal. KSeF certificates and tokens are stored encrypted. In the same place you have VAT registers, JPK_V7M/V7K filing to the Ministry and ZUS contribution calculations with a deadline calendar.

FAQ

Can I issue an invoice only in English in Poland?

Yes, if the buyer is a business. Polish VAT law doesn't specify the language of an invoice. The exception is consumers in Poland, who should receive the document in Polish. Remember that VAT must be shown in złoty, and during an audit the tax office can ask for a Polish translation. That's why many businesses choose bilingual invoices.

Does KSeF accept invoices in a foreign language?

Yes. Field names in the FA(3) schema are Polish and fixed, but the content, such as a service description, can be in a foreign language. The Ministry of Finance also allows an English or bilingual visualisation, provided it matches the XML file in KSeF in substance and includes the QR code and KSeF number.

Does a foreigner with a JDG have to use KSeF?

Yes, citizenship is irrelevant. The obligation depends on your VAT status and Polish NIP. Most JDGs have issued invoices in KSeF since 1 April 2026, and the smallest taxpayers join on 1 January 2027. All VAT payers have had to receive invoices via KSeF since 1 February 2026.

How do I log in to KSeF without a PESEL?

A Trusted Profile requires a PESEL number, so without one you'll need another method, such as a qualified electronic signature or a KSeF certificate. You can also grant a permission to your invoicing software. The details depend on your situation, so check the current instructions at ksef.podatki.gov.pl.

Does an invoice for a foreign client also have to go through KSeF?

As a rule, yes, if KSeF applies to you. You issue the invoice in KSeF and deliver a visualisation to your foreign client in an agreed way, for example a PDF by email. The visualisation must include the QR code and KSeF number. It can be in English if it matches the XML data.

What is the penalty for issuing an invoice outside KSeF?

From 1 January 2027, up to 100% of the VAT shown on an invoice issued outside KSeF, or up to 18.7% of the total amount due for an invoice without VAT (Art. 106ni of the VAT Act). The tax office scales the penalty to the seriousness of the breach. No administrative penalties are imposed in 2026.

Summary

Choosing invoicing software in English in Poland, or in Ukrainian, is a legal and sensible choice for a foreigner running a JDG. Your interface can be in any language. A B2B invoice can be in a foreign language, but VAT must be shown in złoty, consumers get a Polish document, and the visualisation must match the XML in KSeF. The simplest way to get all of this right is a bilingual invoice generated automatically from KSeF data.

This article is for information only. For your individual case, it's worth consulting a tax advisor.

If you're switching invoicing software before 1 January 2027, you can try Biurko on the FREE plan: no card required, unlimited KSeF submissions and an interface in Polish, English or Ukrainian.