Top 20 language is an, uh, interestingly narrow request. Is being the first computer programmer ever[0] not enough impact?
In programming languages there's of course Grace Hopper, one of the early advocates for machine independent languages, who implemented the first linker[1], and also created FLOW-MATIC[2], the first english-like data processing language. FLOW-MATIC was was a major inspiration for COBOL which, incidentally, was partially developed by Jean Sammet, also a woman.
