Most languages, or better, most scripts do not have upper and lower cases letters. Only four use them: Roman (the one I'm using now), Cyrillic (used for Russian, some other Slavic and also many Central Asian languages), Greek, and Armenian.
None of the scripts used for Semetic have this difference: Arabic, Hebrew, Amharic, etc.
None of the scripts used for the Indic languages this difference: Devanagari, Gurmukhi, Bengali, Oriya, Gujarati, Kannada, Telugu, Malayalam, Tamil, Sinhala.
None of the languages of Souteast Asia, whose scripts are borrowed from the ancient Brahmic script have this difference: Burmese, Thai, Khmer, Javanese, etc.
None of the writing systems of East Asia make this distinction: Chinese hanzi, Japanese hiragana and katakana, Korean hangul.