For series titles...
As much as possible, the official Japanese name is used, unless it is super obscure.
The anime news network is used as the reference guide for what are the official names and the English translations.

For set codes...
1. Use Japanese offical names.
2. Where no Japanese official name is available, use the most commonly used term in the English trading card community. (but be ready to change it, or mention alternative names)
3. No official name, no agreement, come up with a name and put it in (). Mention this in the set info.