Multiple-to-multiple glossaries are the most complex type of glossaries. Several, related source terms are related to a target term and its alternatives with different stylistic levels, client preferences etc.
Though glossaries of this type look complex, they actually can reduce the amount of time that you have to invest to build a glossary.
Use the semicolon both for separating source terms from each other as for separating target terms from each other.
PLEASE NOTE: You shouldn't use Glossary > Merge alternative translations for this glossary type.