Go back to the main menu
If you cannot find language selection in the in-game pause screen, return to the Main Menu. The official 1.0.30 announcement says the added localization languages are only selectable via the Main Menu. Select the language you want to use.
The announcement establishes the menu mode, but not a detailed submenu path. A specific Settings > General > Language route was not observed and is not provided here.
Languages in the announcement
The update adds Simplified Chinese, German, Italian, Ukrainian, Spanish (Spain), Japanese, Russian, Korean, Spanish (Latin America), Brazilian Portuguese, French, Turkish and Polish. This is the announced localization range, not a promise that every translated line is flawless.
Keep your progress in mind
Finish the day’s settlement and advance to the next save point before returning to the menu. This is a progress-preservation suggestion, not proof of immediate saving during any round.
After selection, check the menu text, then enter the save and check major prompts. Console commands, Windows language and Steam interface language are not substitutes for this in-game choice. Earlier builds cannot be assumed to have languages added by 1.0.30.