I actually am not a big fan of the wand theory, personally I think spell creation, and the spell's power ultimately relies on the person's ability to pronouce the spell. That is why way way back they decided to make spells in Latin because people were more familiar with it. I guess traditions stuck and that being the reason as to why most spells are spoken in latin.
Note: the spell's ultimate purpose is to do something, so the intention is important right. Now for example say we take wingardium leviosa, a person who struggles saying this spell would struggle performing it. However if someone who with the intention of lifting something commands their magic to do so by firmly saying 'lift' in their fluent language, it would be more efficient and powerful. What I am saying is that, wands makes magic flow easier however the magic comes from the person not the wand or language the spell is spoken in. The more comfortable the person is saying the more powerful it is going to be.

 

I always thought that spells were a manifestation of faith. Enough people believe that saying "Alohomora" opens a door, so it does. Wizards create spells through either sheer will power of believing a spell into existence or by convincing large groups of people he already invented the spell, and then using it.