equivalent of proper noun!

Hi. Can proper nouns of a native language be translated in the target language? for example the name of a language institute?

It depends on the language and the circumstances.
Place names, for example, are often translated.

Let me give you an example. In Arabic “sea” is called “bahar” Now suppose that there is a language institute with the name of “Bahar Language Institute”. In that area every one knows it under this name, but on the tableau of this place " Sea Language Institute" is written! While no one call it under this name there! Is it possible to use equivalent here?

I don’t know what you mean by the ‘tableau of this place’, but if the institute are billing themselves in that way, then opbviously it is up to them if they wish to be bilingual.

I don’t know what you mean by the ‘tableau of this place’, I meant the board set up out of the building to show its name.

I’d call that a sign, rather than a tableau.
In that case, the Institute is entitled to write their name in any language it wishes.

Even if every one going to that place uses its equivalent in their native language not the translated one printed on the sign?

It’s the Institute’s choice if it is their name.