Latin Extended-B Languages?

Hey there, 

I wanted to know which languages are part of the Latin Extended-B set. I can find the glyphs but not the languages that they support.

Are they very 'important'? Or should I focus on other languages like Cyrillic/Greek?

Up to now, no client has ever asked for Latin Extended-B, never the less, a lot of 'pro' typefaces seem to have his character set covered.

Thank you