This is not a duplicate of bug439205 but a regression of that fix when using LanguageTool locally. I informed about this about 1 year ago https://bugs.kde.org/show_bug.cgi?id=439205#c13 but my comment did not get attention. The issue is that the list of available languages are looked at: https://api.languagetoolplus.com/v2/languages/languages, which returns the following error: Error: Unsupported action: 'languages/languages'. Please see https://languagetool.org/http-api/swagger-ui/#/default Instead, the list of available languages should be looked at: https://api.languagetoolplus.com/v2/languages, which returns the proper list: [{"name":"Arabic","code":"ar","longCode":"ar"},{"name":"Asturian","code":"ast","longCode":"ast-ES"},{"name":"Belarusian","code":"be","longCode":"be-BY"},{"name":"Breton","code":"br","longCode":"br-FR"},{"name":"Catalan","code":"ca","longCode":"ca-ES"},{"name":"Catalan (Valencian)","code":"ca","longCode":"ca-ES-valencia"},{"name":"Chinese","code":"zh","longCode":"zh-CN"},{"name":"Danish","code":"da","longCode":"da-DK"},{"name":"Dutch","code":"nl","longCode":"nl"},{"name":"Dutch","code":"nl","longCode":"nl"},{"name":"Dutch (Belgium)","code":"nl","longCode":"nl-BE"},{"name":"English","code":"en","longCode":"en"},{"name":"English","code":"en","longCode":"en"},{"name":"English (Australian)","code":"en","longCode":"en-AU"},{"name":"English (Australian)","code":"en","longCode":"en-AU"},{"name":"English (Canadian)","code":"en","longCode":"en-CA"},{"name":"English (Canadian)","code":"en","longCode":"en-CA"},{"name":"English (GB)","code":"en","longCode":"en-GB"},{"name":"English (GB)","code":"en","longCode":"en-GB"},{"name":"English (New Zealand)","code":"en","longCode":"en-NZ"},{"name":"English (New Zealand)","code":"en","longCode":"en-NZ"},{"name":"English (South African)","code":"en","longCode":"en-ZA"},{"name":"English (South African)","code":"en","longCode":"en-ZA"},{"name":"English (US)","code":"en","longCode":"en-US"},{"name":"English (US)","code":"en","longCode":"en-US"},{"name":"Esperanto","code":"eo","longCode":"eo"},{"name":"French","code":"fr","longCode":"fr"},{"name":"French","code":"fr","longCode":"fr"},{"name":"Galician","code":"gl","longCode":"gl-ES"},{"name":"German","code":"de","longCode":"de"},{"name":"German","code":"de","longCode":"de"},{"name":"German (Austria)","code":"de","longCode":"de-AT"},{"name":"German (Austria)","code":"de","longCode":"de-AT"},{"name":"German (Germany)","code":"de","longCode":"de-DE"},{"name":"German (Germany)","code":"de","longCode":"de-DE"},{"name":"German (Swiss)","code":"de","longCode":"de-CH"},{"name":"German (Swiss)","code":"de","longCode":"de-CH"},{"name":"Greek","code":"el","longCode":"el-GR"},{"name":"Irish","code":"ga","longCode":"ga-IE"},{"name":"Italian","code":"it","longCode":"it"},{"name":"Japanese","code":"ja","longCode":"ja-JP"},{"name":"Khmer","code":"km","longCode":"km-KH"},{"name":"Norwegian (Bokmål)","code":"nb","longCode":"nb"},{"name":"Norwegian (Bokmål)","code":"no","longCode":"no"},{"name":"Persian","code":"fa","longCode":"fa"},{"name":"Polish","code":"pl","longCode":"pl-PL"},{"name":"Portuguese","code":"pt","longCode":"pt"},{"name":"Portuguese (Angola preAO)","code":"pt","longCode":"pt-AO"},{"name":"Portuguese (Brazil)","code":"pt","longCode":"pt-BR"},{"name":"Portuguese (Moçambique preAO)","code":"pt","longCode":"pt-MZ"},{"name":"Portuguese (Portugal)","code":"pt","longCode":"pt-PT"},{"name":"Romanian","code":"ro","longCode":"ro-RO"},{"name":"Russian","code":"ru","longCode":"ru-RU"},{"name":"Simple German","code":"de-DE-x-simple-language","longCode":"de-DE-x-simple-language"},{"name":"Slovak","code":"sk","longCode":"sk-SK"},{"name":"Slovenian","code":"sl","longCode":"sl-SI"},{"name":"Spanish","code":"es","longCode":"es"},{"name":"Spanish","code":"es","longCode":"es"},{"name":"Spanish (voseo)","code":"es","longCode":"es-AR"},{"name":"Swedish","code":"sv","longCode":"sv"},{"name":"Tagalog","code":"tl","longCode":"tl-PH"},{"name":"Tamil","code":"ta","longCode":"ta-IN"},{"name":"Ukrainian","code":"uk","longCode":"uk-UA"}]