Is it really advisable to file nationally again within Europe? After all, the objective of this approach is to keep the German or other national infringement courts for litigation. However, in the Agreement on a Unified Patent Court (UPC) there are a few relevant regulations concerning this question.
Once a European patent has been granted, the validity of the unitary patent can be requested for all states of the EU that have ratified the UPC up to that point, meaning those for which the UPC agreement and the EU regulation are in effect. This request must be submitted to the EPO - together with a translation, at least for the time being - within one month following the mention of grant (Art. 9 Sec. 1 g), Regulation (EU)).
But that is only an option. You don’t have to do it. You can stay with the “classic” European patent and validate traditionally. You will do this anyway if you only want protection for a few countries, since the unitary patent will only pay off if there are four or five countries or more, the exact number of countries depends on the office fees, which are still under discussion.
Now, the unified patent court system is also valid for “classic” European patents (Art. 32 tog. with Art. 2, letters e), f) and g), UPC Agreement). That is precisely what makes up the compulsory nature of the new court system.
However, it is possible to choose to opt out under Art. 83, Sect. 3, UPC. You can declare before the Registry of the court that you wish to stay with the old court system. And this can be done up to one month prior to the end of the transitional period pursuant to Art. 83, Sect. 1 or 5 UPC (Art. 83, Sect. 3 UPC).
And you can even declare this opt-out for European patent applications (Art. 83, Sect. 3, Sentence 1 UPC)!
This means you can still file an application(!) for a European patent several years from now, until shortly before the transitional period expires, and still keep the old court system for this patent application all the way to the end of the life of the patent.