What is the Latin translation for that is?

The prepositions 'de' or 'e' can both be used. 'E' turns into 'ex' when the next Word starts with a vowel. However, Latin does not generally use a preposition to show possession but instead places the Word into the genitive case, thus if one were to say something like 'capital of California' it would be rendered 'caput Californiae' where the 'of' is contained in the inflected ending of California. Note that the inflection has not simply added an 'e' to the end of California, rather the 'a' has been replaced with '-ae' which is the genitive ending for the group of Words (declension) that California (probably) belongs to. Other Words may have different genitive endings depending on which declension they belong to, an example being 'Angus Dei' (Lamb of God) where the Word 'Deus' has had its '-us' ending replaced with the genitive '-i' of the declension which it belongs to.