gui design – Decrease the font size or break to a new line with multiple languages?

Languages that have accents in their alphabet will benefit from an increase in line-height. When you have a lot of accents they can get ‘caught’ with descenders of the glyphs above.

Second of all, some languages that are not latin based, for instance Arabic will benefit from a slightly bigger font size. This will then dictate your line-height.

Remember the so called typographic triangle where the measure (the number of characters per line) competes with the font size and it’s line-height. Plus you have to take into account the typographic hierarchy; so headers (H1-H6), paragraphs, lists etc.

Finally when you have a responsive website it gets even more complicated with device width. Smartphones will benefit from a slightly bigger font than desktop so this will feed into the measure and line height. There are lots of solutions out there, mostly SASS/SCSS based but it takes some work.