It cannot be a language - in reference to Koen's latest video

[Jorge_Stolfi]

Vowel length, phonetic in Japanese, can also been marked with a diactiric,

In hiragana, long vowels are marked by adding an extra pure-vowel character: 
  ま = ma, あ = a, まあ = mā
  と = to, う = u, とう = tō
Syllables with vowel "-o" should logically be lengthened with お = o, but う = u, is traditionally used instead. 

In katakana, vowel lengthening is indicated by a dash:
  ト = to, トー = tō

Besides the two diacritics described in the previous post, hiragana and katakana use a small subscripted prefix, つ or ツ respectively, to indicate Italian-like "doubling" of the following consonant:  
  かっこ = kakko = parentheses
  かこ  = kako = the past

All the best, --jorge