What language is used in equations in Pages and Keynote? e.g. \texttt{}, \mathtt{}, \tt{} and \text{}
Pages supports equations written with both LaTeX commands and MathML elements. However, it doesn't support all of each language providing only a subset of available features.
In regards MathJax, it is actually also the case that MathJax supports LaTeX and MathML markup, so that's why you'll find that commands used with MathJax also work with Pages. The environments, configurations, installed packages, and so on, are not the same however, and that's why you'll find inconsistencies in how the same lines of code are displayed in the two systems.
You'll find Apple's documentation for the feature here:
https://support.apple.com/en-gb/HT202501
There are no options to change which languages are supported by equations in Pages.