Have you even looked at the capabilities of ePub3 metadata? Heck, ePub2 allowed opf:role="trl" while ePub3 uses refines for a contributor to specify a translator or original book information
Code:
<dc:contributor id="translator01">Ann Onymous</dc:contributor>
<meta refines="#translator01" property="role" scheme="marc:relators">trl</meta>
and optionally:
Code:
<meta refines="#translator01" property="file-as">Onymous, Ann</meta>
For the original title, use a title element with a refines to indicate the original title:
Code:
<dc:title id="t1">The Metamorphosis</dc:title>
<dc:title id="t-original">Die Verwandlung</dc:title>
<meta refines="#t-original" property="title-type">main</meta>
Yes, the src-title-info may be a bit simpler but ePub2 nevermind ePub3 are fully capable of storing metadata for a translated book.
The next question is whether any reading software can make much use of either format's metadata. I do know that a while back, people were complaining that while FB2 had the sequence metadata for series/series index, the reading programs did not seem to make use of the info.