In the Bulgarian language, we have a letter "Ъ" (capital, U+042A) and "ъ" (small, U+044A). It sounds like mixture between "A" and "O" in English. Commonly it is transliterated as "A" or "a". Currently, the library transliterates it as "'", which is wrong and does not stand for any sound (phoneme).
The same issue is with letter "ь" (similar to Russian soft sign U+044C). It has no capital case and is always used before "о". Currently it also is transliterated as ' (wrong).

To do:

• "Ъ" and "ъ" should be transliterated as "A" and "a"
• "ь" should be skipped in any case without subsequent "o" and when it stands before "о", both letters, e.g. "ьо" should be transliterated as "yo"

Examples:
Петър -> Petar (now is Pet'r.)
България -> Balgariya (now is B'lgariya)
Кольо -> Kolyo (now is Kol'o)