The closing single quotation mark is identical or similar in form (depending on the font) to the apostrophe and similar to the prime symbol.The double quotation mark is identical to the ditto mark and similar to—and often used to represent—the double prime symbol.The German tradition preferred the curved quotation marks, the first one at the level of the commas, the second one at the level of the apostrophes ().
The single quotation mark emerged around 1800 as a means of indicating a secondary level of quotation.
One could expect that the logic would be the corresponding single mark everywhere but it was not the case.
Such fonts are therefore typographically incompatible with this German usage.
Double quotes are standard for denoting speech in German.
with the 'English-style' quotation marks being preferred.