[e] and [ε] are pronounced almost the same in English. But there is obvious difference between them in french , french [e] sounds like ‘ay’ in english ‘bay’, really close to the first English letter “A”—-[ei]. Why french [e] and english [e] are pronounced differently? Dont western languages share the same International Phonetic Alphabet ?? Or they share the same IPA but their pronounciation are different?
I'm a bit confused by these questions. [e] and [ε] are not pronounced almost the same in English.
hate /heɪt/ bet /bɛt/
It seems like you're referring to letters, not sounds. When you use brackets , it's is supposed to be referring to sounds, not letters, so if the phonetic transcription is accurate, there shouldn't ideally be much difference between [e] in different languages. That's the whole purpose of IPS is to talk about sounds no what letters represent different sounds.
I may be misunderstanding your question, however. If you have the experience of french linguists using [e] and anglophone linguists using [e] and they ACTUALLY sound different, then I imagine this is either an error, or the result of some kind of academic siloing. It's quite hard to capture all sounds with symbols, and sometimes a language's sound is not quite "exact" for a specific IPA symbol. But they shouldn't be so different as to clearly represent different phonemes, especially one that there is already an IPA symbol for.
IPA is in principle international and universal. However, no phonetic transcription ever reflects all the phonetic niceties of any language. Instead, IPA aims to represent the most salient features of a given language; this is true of phonetic transcription and all the more so of phonological transcription. For example, French “tête” and English “tit” will both be transcribed with twice /t/ (in phonological transcription) and with twice [t] in phonetic transcription, although the sounds are very different in the two languages: French [t] is an unaspirated dental, while English [t] is an aspirated alveolar. But as there is no phonological distinction between dentals and alveolars in either of these languages this difference is generally ignored even in a relatively close phonetic transcription.