[GianFabien]

I am a non-native speaker of English and several other European languages.

English is the hardest to perfect, because of the numerous loan words which defy any systematic rules for correct pronunciation when you read. Then you also have the problem of accents and dialects. Even within a single country there are differences. In the USA: New York vs New Orleans, in the UK: London vs Manchester or Ireland / Scotland.

You could record some TV or radio program, repeat what you hear onto a recording and compare. Best approach would be to get a speech coach. They will explain correct mouth, tongue, etc placements.