Well, I’m no historian but with the case of translations there are always things that are translators choices, since no two languages are exactly alike. Different translators make different choises and others are more exact and others not so.

Reasons for this are varied. First obviously is the skill of the translator(s). The second if the base texts that are used (there are a few in case of the bible). The third is what emphasis the translators want. Do they aim for word to word type translation or more something like paraphrasing (focusing more on underlying meaning or the perception of it) of the text. And obviously as fourth, translators do also make just genuine mistakes.

So saying that there are mistakes in the translation is kind of difficult or even redundant. Many things are perceived as mistakes by some scholars and others defend the translation choices.

When it comes to Mary being virgin, there is no mistake in translation that I’m aware of. In Luke 2:17 for example, the word often translated as virgin (παρθένος ) has both a meaning of being a young unmarried female and a virgin. The idea being that since the girl is unmarried, she has not had sex.

This means, that when a translator uses word “virgin” he is absolutely correct but the word does not fully cover the full meaning of the original word. And similarly, a translator going with “unmarried young girl” is not incorrect either but for modern readers, that does not reflect the concept of the time of unmarried equaling virginity.

Hope this helps. Also hope it’s ok to answer here even as I’m not even remotely an historian.