If your standard.dic in the user profile, folder /wordbook looks has a language set, like: OOoUserDict1 lang: de-DE type: positive you can only add words to your personal dictionary which have the language de-DE. If you try to add words in another language, it's not possible, because the button "Add to dictionary" is disabled (in the Spelling Dialog, Tools->Spelling in Writer). This surely can be improved. We should either automatically create a new dict with the selected language, or at least inform the user why the words can't be added.
No repro, I can add a word in English in my french dictionary in Writter. In the Tools menu, I can add a foreign word via the Spelling Dialog. Or when I right-click on the foreign word, I can indicate add to the dictionary. Version: 7.6.0.0.alpha0+ (X86_64) / LibreOffice Community Build ID: c4a58634753a84b09f20f7271d6525a6656522d3 CPU threads: 4; OS: Windows 10.0 Build 19045; UI render: Skia/Raster; VCL: win Locale: fr-FR (fr_FR); UI: fr-FR Calc: CL threaded
I believe the closing of this was a misunderstanding, but I don't have time to test now. In any case, one should only close as worksforme, if reproducing in an older version.