Sometimes I make my own typefaces. Most of the fonts are very incomplete. I concentrate a-z, A-Z, 0-9 and some punctuation marks. I want to make a more complete font. But find it hard to decide which glyphs to design.
It seems logical to design Latin and Latin Extended A first. But just going for a complete unicode plane seems a bit rough. General punctuation has some very common glyphs, but also some obscure ones that are often omitted.
Are there guides on which glyphs to design? Are there methods to decide which ones? Are there language sets? How do you decide which glyphs to design?
I'm looking for a classification system for glyphs or methods that type designers use to decide what glyphs to design. A graphic designer in Germany will only buy a font if it contains a ß glyph. I'm at the other side of the counter. I design a font for a market. How to know the needs of a market?