Filing a European patent application raises a question that surprises many first-time applicants: which language will your case actually be conducted in? At the European Patent Office (EPO), the answer is governed by Article 14 EPC, and the choice has lasting consequences for cost, procedure, and even whether your application survives. This guide explains the EPO’s language rules, how your language of proceedings is fixed, and the practical decisions that flow from it.
The EPO’s three official languages
The European Patent Office has three official languages: English, French, and German. These are set out in Article 14 of the European Patent Convention. Nearly all substantive proceedings before the EPO are carried out in one of these three, and the office’s working documents, search reports, and communications are issued accordingly.
This is one of the procedural details that catches applicants off guard when they move from a national filing to a European one — alongside the office’s strict formal rules, such as the EPO drawing requirements under Rule 46 EPC.
Filing language and translation (Article 14(2))
You are not required to file in English, French, or German. Under Article 14(2) EPC, a European patent application may be filed in any language. However, if you file in a language that is not one of the three official languages, you must supply a translation into one of them within the period set by the Implementing Regulations.
This flexibility comes with a hard deadline. If the required translation is not filed in time, the application is deemed withdrawn — a harsh but firmly applied consequence. The translation can later be brought into conformity with the application as originally filed, but the obligation to translate is not optional.
How your language of proceedings is fixed (Article 14(3))
Article 14(3) EPC sets the key rule: the official language in which the application is filed — or into which it is translated — becomes the language of proceedings, and it is used in all proceedings before the EPO. So if you file in English, English is your language of proceedings; if you file in Japanese and translate into German, German governs.
One point trips up applicants repeatedly: the language of proceedings cannot be changed once it is set. The Enlarged Board of Appeal confirmed in decision G 4/08 that an applicant cannot switch the language of proceedings to one of the other two official languages later — for example, on entry into the European regional phase from a PCT application already published in an official language. Choose deliberately, because you are committing for the life of the case.
Fee reductions and Article 14(4)
The language rules also contain a benefit. Under Article 14(4) EPC and the related Implementing Regulations, applicants who have their residence or principal place of business in an EPC contracting state that has an official language other than English, French, or German may file certain documents in that national language. Doing so can entitle them to a reduction in specific fees, recognising the burden the three-language regime places on applicants from those states. The document must still be followed by a translation into an EPO official language.
For applicants weighing where and how to file internationally, language strategy sits alongside route selection — see our guide to filing a PCT international patent application, which often feeds into the European phase.
Why the choice matters in practice
Because the language of proceedings is permanent and drives every later communication, oral proceeding, and amendment, it is a strategic decision rather than an administrative one. English is by far the most common choice and gives the widest pool of qualified representatives and translators. The volume and cost of translations, the language skills of your patent attorney, and the languages of the prior art you expect to address all feed into the decision. Getting it right at filing avoids friction — and irreversible limitations — for the years a European application can remain pending.
Frequently asked questions
What are the official languages of the EPO?
English, French, and German, as set out in Article 14 EPC. One of these will be your language of proceedings.
Can I file a European patent application in another language?
Yes. Article 14(2) EPC allows filing in any language, but you must file a translation into English, French, or German within the prescribed period, or the application is deemed withdrawn.
Can I change the language of proceedings later?
No. Once the language of proceedings is set under Article 14(3) EPC it cannot be changed, as confirmed by Enlarged Board of Appeal decision G 4/08.
Do I get a fee reduction for filing in my national language?
Applicants based in an EPC contracting state whose official language is not English, French, or German may file certain documents in that language and claim a reduction in specific fees under Article 14(4) EPC, provided a translation follows.
Which language should I choose?
English is the most common choice because of representative availability and translation cost, but the right answer depends on your attorney, the prior art, and your translation budget. Because the choice is permanent, it is worth deciding deliberately at filing.
Plan your European filing language with care
The EPO’s language of proceedings is fixed at filing and cannot be undone, so it deserves a deliberate decision rather than a default. Contact PerspireIP to discuss your European patent strategy — including the language, translation, and procedural choices that shape the cost and strength of your filing.