Running release of version 20 on Windows 10. I select SPANISH for my subtitle language (my system is English) and only the first six seconds are in Spanish. The rest of the subtitles are in English. I had two subtitle tracks initially, one English and one Spanish. I deleted both tracks and re-ran asking only for Spanish. Same result. Resolve version 20.0 build 49.
You are not using AMD GPU by any chance? The latest AMD driver update (25.5.1) seems not to work properly with transcript generation (albeit tested only in 19.1.4). Had to backtrack to 25.3.1.
Resolve Studio 20.0.0/Windows 10/AMD 5600x/64GB/RX 6600 Resolve Studio 20.0.0/Windows 11/Intel Core Ultra 7 258V/32 GB/Arc 140V