Shcha or Shta (Щ, щ) is a letter of the Cyrillic alphabet, representing the consonant /ʃʲ/, /ʃʧ/, /ʃʲʧʲ/ in Russian, and the consonant /ʃt/ in Bulgarian. Originally, this letter was a ligature of sha and te (Ш + Т = Щ), with the descender in the middle of the sha, and is descended from the Glagolitic letter Shta:
This letter is the most troublesome for transliteration. In English language, it is typically transliteratedShch or šč (with a háček). In German, it requires 7 letters: "schtsch", thus giving rise to a popular joke about a Russian tsarina of German origin that she managed to make 8 mistakes in a two-letter word, "Щи" (a kind of Russian vegetable soup).
There may be special escape characters or sequences to signal the beginning and end of converted strings, but these by preference should be required only in the converted form, not the wide-character standard form.
Obviously the converted strings cannot be understood as specific (strings of) displayed characters, such as Cyrillic capital shcha or Mandarin shi4 (~= 'be'), without knowing the language and code set of each string; but assume that each file contains only English and one other (variable) language, which is known for each file.
Also assume that character representation must remain constant, so that capital shcha is represented by the same ASCII substring wherever it occurs in its string.