In English, we often use common for the adjective equivalent of often. But in Esperanto, the word "ofta" already exist. Does that mean komuna has a different meaning than in English?
The word common in English has multiple possible meanings. Komuna and ofta can both be translated to "common" in English, but "common" can be translated to one or both, depending on the context.
- Ofta refers to things that aren't unusual. A better translation in English might be "commonplace". For example, one might say: "Facilaj demandoj estas oftaj en StackExchange." The adverbial form, ofte, while usually translated as often, can then be thought of as describing an action as commonplace.
- Komuna refers to things which are communal or shared by more than one person or group. The best equivalent I can think of in English is a "common border." One might say that "StackExchange estas komuna demandejo."