"Let drink" is not a correctly spelled word in English. It appears to be a confusion of the two separate verbs "let" and "drink". "Let" has the IPA transcription of /lɛt/, while "drink" has the transcription of /drɪŋk/. To form a grammatically correct phrase, one could write "let's drink," using an apostrophe to contract "let us." This would have the IPA transcription of /lɛts drɪŋk/.