European quotation marks commonly have the left one down low and the right one up high. The same applies for single quotes. But using comma-backtick is deeply unorthodox.
Interestingly, the author does not follow this convention on his personal site (first link in profile) … instead option for the ‘single quote’ form instead.
To give a definite answer to the discussion below - it seems Czech, Slovak, German, Slovenian and Croatian sometimes use this format. Here an authoritative source: the EU publications office:
Both are wrong. tcmb didn’t use ‚comma-apostrophe’ – they opened with , U+201A SINGLE LOW-9 QUOTATION MARK (not U+002C COMMA) and closed with ‘ U+2018 LEFT SINGLE QUOTATION MARK (otherwise known as an open single quotation mark).