Paragraph language has nothing to do with Program Preferences, it is part of the paragraph properties, you should always use Paragraph Styles.
How dis you set up your Paragraph Styles?
Do you use Character Styles?
Do you have manual overrides.
Language is a character-level attribute and can be assigned to isolated strings or single characters to allow proper spell checking and hyphenation of "foreign" text mixed in with the regular text.
Thanks to you and to Peter Spier. Selected text used Character reassigned select text to English.
Worked just tedious but successful.
Now that you've struggled to do it the hard way, it could have been done very quickly using Find/Change and the GREP tab. Find .+ and set the Change Format > Advanced Character Formats > Language dropdown..., then Change All.
With no Find Format qualifiers, this would set every bit of text in the doc to the single language of your choice. Setting the Find Format language to Spanish would find only text already set to that language.
Obviously I'm an InDesign novice. It's been a learning experience; so thank you for an alternative way.
Find/Change, especially with GREP, is one of the most powerful tools you have in ID.