So, why should the English name be used in this situation? Wouldn't the Celtic name be more appropriate? Celtic languages are co-official in Scotland and Wales, while in Ireland, Irish is the first official and national language. Due to this, I would prefer to use placenames such as "Corcaigh", "*An Uaimh*" (for Navan), "*Chill Dara" *(for Kildare), etc. However, this sounds quite odd and are not frequently used, even though they are the first official name. What do others think? I am inclined to use them so that people are actually educated that there exists an Irish language as the first official language of Ireland. Too often, people in Romania say "the Irish speak (just) English" and stop it at that. They're surprised, for example, when I tell them about Irish names such as "Baile Atha Cliath" for Dublin, etc.
The classic answer is that you should use whatever is currently most popular with Romanian speakers, if that can be determined. Wikipedia is descriptive, not prescriptive, about the use of language.
In some situations this will presumably not be very helpful. Romanian is probably not such a difficult case. But for some very small languages, particularly those without a strong written tradition, it will perhaps be impossible to say what the X-language word for Y "really is" based on existing usage. (Because there is no existing usage, or there is not enough written existing usage.)
Probably in such cases, "standard patterns" can be followed. That is, in an African language from a French colonial area, it might make sense to use a French name for a city, whereas in an African language from an English colonial area, it might make sense to use an English name. (This is presuming there is no obvious choice based on existing usage.)
--Jimbo