Is the theta role in one language (ex. English) - L1 the same as in another language - L2, when this two sentence are about the same ? Can anybody give me example, when they are different ?
I believe that theta roles have to be considered universal or else they are a useless concept. By definition they have to do with the underlying meanings and relations in a statement. When it comes to general word definitions it is very difficult to find one-to-one correspondence between languages because ordinary words tend to be polysemous and can have nuanced meanings with various connotations and histories in a language. But when talking about theta roles, or semantic roles as I would call them, we are talking about a purported underlying system in language that is necessary for any language to function at all. Basic concepts like SOURCE, PATH, and GOAL which do seem to be present in all languages (to my knowledge.)
However, that is not to say that "when two sentence are about the same" that the semantic roles in each language will match up perfectly. I don't have any example off hand, because I don't know any second language well enough, but I feel like I can almost think of an example where an expression is translated into another language and in the process the semantic roles have to change. Like the patient in L1 may be expressed as a recipient or something in L2, even though you are translating as directly as possible. Does that make sense?
This isn't an example but it can give an idea of how languages can "think" differently about the same concepts. Some languages like Finnish have no verb for "have" so they instead speak about things as being on someone. Like "minulla on koira" -- literally "on me is a dog".
The answer to this question Thematic roles in some languages seems relevant.