You can select the text frame and change the language in the Control panel
or you can select a specific portion of text, say a word, in a frame and change the language for that in the Control panel.
If you want to change the application’s default language, in a no document state, edit the [Basic Paragraph] style in the Paragraph Styles panel (in Advanced Character Formats) category.r mitchell supported this idea ·r mitchell commented
it appears the UK dictionary includes american spellings (z instead of s for example) as alternates and thus does not pick up words like civilization... i've even added it as a removed word but it's still not found in a spell check using UK english. how can i edit the entire UK dictionary to force the acceptable word list? spell check is useless.