1. I find this acceptable with or without "the". My preference would be to include it.
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OttoJEnglish, of all languages in the world, contains (the) most words. (=It contains the highest number of words)1. Is my sentence natural/correct English? Should I use the?Yes, you should use the. And also with languages. For simplicity's sake I'd put the of-phrase first. You can also use among.