According to post 3, languages other than English do not have the variety of accents that would allow the play to retain its uniqueness. Since I am not a linguist or speaker of any language other than English I can only make an educated guess here, but I really doubt that other globally spoken languages such as French and Spanish do not have a wide variety of accents that depend on a speaker's location and social station. With that in mind, I would think that Pygmalion could probably be adapted to many other languages.
However, I have to admit that if accentual variation is unique to English, then I am wrong.
I think it would be difficult to adapt the play to a language other than English simply because of the scenes which adhere strictly to teaching Eliza the "proper" sounds and accents of the English language. Every language/country has different dialects and accents that are specific to that region, but in order to present the play in another language, the play would have to be rewritten for the accents of that language. In effect, this would change the play to the point of losing its particular uniqueness. The social and relationship issues that are discussed are truly universal and could be applied to any culture or language, but the parts of the play that focus on Eliza's accent would either be hugely misunderstood or have to be rewritten entirely for the sounds and accents to be applicable to whatever audience is watching.
The play is definitely English-driven, but you could adapt it to other countries, cultures and language. At its heart it is a play about social class and the barriers to class mobility. This occurs in any country, culture, or language.