Do spells have to be in well I don't even know what language :p but do spells have to be written in a certain language to work or be more effective? And what language is most common for spells? Thanks
Spells can be written in English. There really isn't a "have to" when it comes to writing spells. If you feel it will increase the spells power and you can speak that language, go ahead. Do what you feel will increase the spell's power and feels right to you.
i personally have some spell books which have been translated into english from ancient languages and they are still extremely powerful but i also have a couple in foreign languages and it's been stated that it is vital to keep them like this less they lose their power. It really all depends on the spell but i wouldn't go messing about with translating certain spells as i am not experienced in this. Best to stick with what you know.
It's very late now, so I'll keep this short, promise. ;)
Witchcraft works because of the ability of the practitioner to raise, focus, and send forth energy for a purpose. The language doesn't matter at all and it could be argued that if the practitioner uses language unfamiliar to her/him it might actually impede the process.
Spell craft is very misunderstood by many people because they don't understand that the spell itself has no power. It takes most people years of practice and study to learn spell craft, and the tools, "ingredients," etc. are simply there to help us focus our intention and to act as sympathetic magical correspondences to aid us in our attempts.
The language is basically something you choose while casting your spells. I'd also like to add that in some spells you do not have to chant anything, simply manipulate and direct your energy for a purpose, which is the basic form of spell craft anyway.
I recommend to have this language as a language you feel comfortable with, because it helps you to focus your energy and manipulate it way better. Do not choose a language just because it seems 'cool' or because it's ancient. You better focus on energy manipulation and proper spell casting than having a cool chant or language.
I also recommend to know the language or at least what you're chanting, because you need to focus on something for a purpose and have an obvious intent.
it's better if you understand it. you need to feel confident while saying it. if you don't know how to pronounce a word, you'll concentrate more on how to say it or what it means instead of the actual spell. same goes for rhyme, a spell doesn't have to, if you feel better using a rhyming chant, then go for it, but if you feel goofie, then go for something else. while the words are important, you need to say them with conviction. so one final point, be sure you choose your words wisely. a common example is when calling upon dragons, don't say something like 'i want you to burn away my enemies' because they will think you seriously mean set them on fire, when you really mean keep your enemies from getting in your way. so watch your wording.
the most common, maybe because i'm English, but English [Elizabethan most of the time] but Latin is another one i do come across a lot, Gaelic, Egyptian, seen a couple written in other languages, but i think it's because the people speak said language so they wrote it in their native tongue.
If you say spells correctly in ancient languages they work. Most commonly i've noticed is spells said in english dont often work. So i stick to most of my spells said in enochian and a type of 'magic toungue' (as some would call it)
Spells merely channels magic into action, they are not magic in and of themselves. They don't even need to be spoken, you just need to believe they will work. The only benefit of learning spells, rather than crafting your own as you need them, is in case someone else thought of one that more effectively focuses your thoughts. The words are just there for your convience.
Note: This does not apply to rituals, which must be performed precisely as instructed to work properly.