There are two places to look:
First: Check the “Dictionary” section of Preferences dialog box. What are the single- and double-quote options set to?
Second: select the text and check what language it’s set to in the character formatting section of the Control panel (or Character or Properties panel). If it’s set to, say, “French,” then you’ll get different quotes than if it’s set to English.

When do you see the error appear? Is this a single InDesign document, or are you trying to create hyperlinks from one document to another (which I don’t recommend). Another way to handle hyperlinks is to set a hyperlink destination first (like an anchor) and then create a hyperlink to jump to it.

Khara Plicanic also wrote about making digital planners in InDeisgn in this (member-only) article:

All About Digital Planners

InDesign’s gradient’s usually work great. But another option would be to go old school and create the gradient in Photoshop, then import it as a PSD into InDesign.

Vietnamese uses a number of very specific glyphs that do not exist in most fonts. You would probably need to get a special version of Garamond that includes those characters.

Adobe Fonts says that Garamond Premiere supports Vietnamese, but… not sure. Worth looking at, at least:
https://fonts.adobe.com/fonts/garamond-premier