For a glossary of terms: https://github.com/jagracey/Awesome-Unicode/blob/master/GLOSSARY.md

For everything about Unicode: www.unicode.org/ http://www.unicode.org/charts/
Example: You want to typeset (or learn about!) "Cuneiform Numbers and Punctuation".
The site tells you that these correspond to the range 12400 -- 1247F and you see all the symbols.
In addition there is a precise definition of each symbol.
         You can download the charts for private use.
         You have to find an appropriate font yourself.

Type in a symbol to find the Unicode identification:
http://www.babelstone.co.uk/Unicode/whatisit_fr.html

Choose a language and pick from the virtual keyboard:
http://www.babelstone.co.uk/Unicode/babelmap_fr.html

If you can not type a symbol, then draw it: http://shapecatcher.com/

Various input methods: http://hapax.qc.ca/

Usage: copy and paste ff into a terminal and replace * by the name of the font:
fntsample    -f     *.ttf
                    -o    *.ttf_[fnt_sample_chart].pdf

example:
fntsample -f   DejaVuSerif-BoldItalic.ttf
                -o   DejaVuSerif-BoldItalic.ttf_[fnt_sample_chart].pdf

If you do not have a font, whose name you know: http://www.identifont.com/

Wikipedia has a list of open-source fonts:
https://en.wikipedia.org/wiki/Open-source_Unicode_typefaces

I have used fonts from the following, and other, sources. I have placed a selection of PDF tables
in the directory FONTS+UNICODE/SPECIFIC_FONT_TABLES:

Libertine Fonts. I use the serif version as my main type: http://libertine-fonts.org/

Dieter Steffmann has many, very interesting and finely crafted, fonts:
http://www.steffmann.de/wordpress/test-2/

The League of Moveable Type: https://www.theleagueofmoveabletype.com/ has Raleway and other nice fonts.

Hack is an excellent mono space (teletype =\tt or fixed spacing) designed for coding:
https://sourcefoundry.org/hack/

Various fonts such as "Old Italic": http://scholarsfonts.net/

If you need a glyph and can not find another font that has it, then Unifont is for you!
"[There are] ... glyphs for every printable code point in the Unicode Basic Multilingual Plane (BMP).
The BMP occupies the first 65,536 code points of the Unicode space, denoted as U+0000..U+FFFF."
http://unifoundry.com/unifont/index.htm
For more on Unifont, see: https://savannah.gnu.org/projects/unifont

My main interest is in biblical Hebrew and ancient semitic scripts and in addition I am in the process of learning to read modern Arabic.

For the biblical texts I use the Society of Biblical Literature SBL Hebrew Font:
https://www.sbl-site.org/educational/biblicalfonts_sblhebrew.aspx

This is the default font at: http://tanach.us
This excellent site has the most up-to-date electronic version of the Lenningrad Codex.
You can copy portions of the Bible off the screen, then paste them into the [FORM_for_RIGHT_to_LEFT.tex]
and obtain very eloquent versions using XeTex.

For detailed instructions on how to use tanach.us, see: http://web.ncf.ca/en493/JUDAICA/judaica.html

Other Hebrew fonts and ancient semitic fonts are available at: http://culmus.sourceforge.net/

There are also Hebrew fonts available at: https://opensiddur.org/help/fonts/

For Arabic one can obtain the Scheherazade font at: https://software.sil.org/scheherazade/

SIL has been developing scripts for various languages and also fonts which are aimed at literacy groups: https://scripts.sil.org/

Xetex was developed in the 1990s by Jonathan Kew who was at SIL; see the interview with him at: http://tug.org/interviews/kew.html

A wide variety of fonts and a great deal of information are available at Chris Harvey's site:
http://www.languagegeek.com/