I have mentioned a problem with sans serif fonts. I have found it again. The Islamic State (IS in English) is el Estado Islámico in Spanish, which has the abbreviation EI. However, in a sans serif font, as us used by El País for example, this is virtually indistinguishable from the definite article El, which precedes it. The fist image is clipped from Firefox at maximum size.
I saved that image and then increased it to 1200%. There is a very slight visible difference at this magnification but nothing like enough to be seen when read in normal size. So readers have El EI written confusingly as two identical words.Click to enlarge.