Recently I posted a question about marriage. I have added tag "marriage". Someone edited it and added tag "Nikah". But they mean the same thing (but different in language). (may be they are called tag synonyms) As people from different region prefer different languages is it valid to keep 2 tags with same meaning?
The practice on similar sites (e.g. Judaism ) is to make the English word a synonym for the transliteration. In that case the tag marriage on a question will be automatically replaced with the tag nikah.
StackExchange provides a mechanic where two tags can be tied together as synonyms, such that (for example) tagging anything as either nikah or marriage would be equivalent, and searching for one would bring up all questions tagged with the other.
As far as I know, the ability to propose new tag synonyms is granted with the moderator tools, which are accessible to all users on private beta if they have 1000 reputation (and I believe 2500 reputation once we're in public beta). Synonyms can only be forged when both of the tags in question are already in use; by the time we have enough users with sufficient reputation, there should be enough questions under both tags to make it clear that they are actually synonyms.