Language is a Character-Level attribute. You can reset it in your Paragraph styles and your Character Styles. (or in Paragraph and Character attributes, if you didn't use styles in your document)
Yes, but how do you change it? There is no menu in Character or Paragraph Styles related to Dictionaries.
Type/Character. At the bottom you'll see language. Change it there.
You should only change it in the styles, Change it in the paragraph style, character style is only for exceptions.
It is found in extended character attributes.
Your question indicates that you are not familiar with the use of styles.
Be aware, that NO text should be formatted without paragraph style, no exception in the formatting for several glyphs or words should be done without character style. This is VERY important. Please become familiar with styles, not only Paragraph or Character Styles, also with Object, Table and Cell Style. It is important.
Advanced Character Formats > Language
This choice decides which language's dictionaries are used for spelling and hyphenation and user dictionary.
For spelling and hyphenation you can choose between different providers for each language separate. You could also buy additionally dictionaries from other providers.
There you can set the apostrophes too, for each language separate. But in the text language is a character property, which you have to specify in paragraph styles, for exceptions in character styles.
LoL, I've been through that submenu many times, and never seen it before. I guess it was wrong idea to put a language choice in the submenu that was meant for character formating and it's geometric transformations.