Problem: The usual and preferred work flow is to use the pull down font menu to try a few fonts for particular uses within documents. There are many frustrated posts in various places about the default behavior of LO, especially with Writer but any application that allows user choice of fonts, that the fonts list has every font in the OS. Many beginners make this observation, and they often do not know how to post the problem. This LO behavior makes the fonts menu a mess. The main but not only problems are foreign language fonts, e.g. installed by the OS, a browser, etc., which makes using the fonts list in LO annoyingly tedious. Templates are a partial work around, not always practical.
Suggestion: While researching and deleting some fonts can help, there can be dependencies issues. One can use ~./your_config_directory/fontconfig/font.conf to broadly reject fonts for a user, although this can cause dependencies problems between applications for that user, e.g. LO versus browser. See: https://wiki.archlinux.org/index.php/Font_configuration#Whitelisting_and_blacklisting_fonts , which offers useful code examples, and other posts online. Application specific configuration is often the better approach.
First, it would be so helpful now to be able set up or at least have LO read a similar xml file to blacklist (reject) fonts from LO in the user's HOME LO configuration directory. LO using the same format file as the OS reads to block fonts would help users a great deal, and LO Help could reference links or content in links like the one above.
Later, even better but not as pressing an issue, might be managing fonts from within LO with a nice interface to edit that xml file to achieve this. It might include a tick box list to allow the user to choose which fonts will appear in the font pull down menu with "select all" and "block all".
Joseph, thank you for your ideas to improve LO. There is already a proposal to improve situation  and some bugs, that are relared to this (bug 90161 and bug 91130). So I close this bug as a dublicate. Please feel free to reopen it with a short reasoning, if you disagree.
*** This bug has been marked as a duplicate of bug 91130 ***