If I registered for the bitcointalk signature bounty campaign on April 25, does it mean that only posts beyond that date will be counted?
Yes.
Also, is the post going to be counted if it is in a native language? For example if I post under Philippines thread.
This is not prohibited in the rules, however, be aware that in topics where there is very little traffic, posts may be rejected.
ADDITIONALLY, writing on topics related to BlockChain Hotels is also not calculated for obvious reasons.