Where the previous application claimed as priority is not in an official language of the EPO and the validity of the priority claimed is relevant to the assessment of the patentability of the invention concerned, the EPO shall invite the applicant for or proprietor of the European patent to file a translation into an official language of the EPO within a period specified. The duration of this period will vary depending on the stage of proceedings at which the invitation is sent (see the subsequent subsections).[Art. 88(1); Rule 53(3); ]
Source: http://www.epo.org/law-practice/legal-texts/html/guidelines/e/a_iii_6_8.htm
Date retrieved: 17 May 2021