As indicated in this link, publication of the grant of the European patent triggers a 3-month term for completing validation formalities (applicable to most of the Designated States) in the countries where the protection rights conferred by the European patent are to take effect and that are members of the European Patent Convention. Likewise, when extension fees and/or validation fees have been paid together with the designation fees, the extension/validation formalities for the respective States need also be completed at this time so that protection rights take effect in these States as well.
The Contracting States of the European Patent Convention are the following: AL, AT, BE, BG, CH, CY, CZ, DE, DK, EE, ES, FI, FR, GB, GR, HR, HU, IE, IS, IT, LI, LT, LU, LV, MC, MK, MT, NL, NO, PL, PT, RO, RS, SE, SI, SK, SM and TR.
Regarding validation formalities, following the entry into force of the London Agreement there are three different groups of Contracting States:
a) Contracting States which have NOT signed the London Agreement.
AT, BG, CY, CZ, EE, ES, GR, IT, MT, PL, PT, RO, SM, RS, SK, TR
Validation formalities must be completed and submission of a translation of the entire text of the patent is in most cases required. Otherwise, the European patent will be deemed void ab initio for the corresponding State.
b) Contracting States which have signed the London Agreement:
BE, FR, GB, CH, DE, IE, LI, LU, MC.
Submission of a translation of the text of the patent is no longer necessary since the granted European patent is automatically regarded as a regular national patent. Thus, no further action would be required (apart from payment of yearly maintenance fees).
However, it may be advisable to ask a local patent attorney to appoint himself as an address of service before the local Patent Office in order to receive any eventual notification regarding the national patent.
c) Contracting States which have signed the London Agreement BUT submission of a translation of the claims is still compulsory. Otherwise, the European patent will be deemed void ab initio for the corresponding State, pursuant to Art. 65(2) EPC:
AL, DK, FI, HR, HU, IS, LT, LV, MK, NL, NO, SE and SL.