is there a ring of human influence in BG1? Do you think that charisma is necessary/important in BG1? if so, how much? (for a fighter) 14 will do the trick?

Charisma seems hardly important in BG1. The only notable effects are when the charisma of the main character (you) is 18 or (I think) lower than ten. Even so, the effects are usually small and not truly worth spending points on. For example, when you take up Garrick's offer and hire out to Silke, she offers to pay you 300 gold for your services. With a low charisma, she only offers 200. With a charisma of 18, she offers 400 gold.
Similarly, a charisma of 18 will get you a book upon returning the belt from the ogre (again, if I recall correctly) and some potions of antidoe if you decide to empty the house in Beregost of the spiders inside.
A charisma of 17, however, hes no such effect.

As for rings of influence, there are none. Still, some magical items give you a +1 bonus while worn, and there are the tomes with which to increase it by one point permanently.

The only other reason, besides the small bonusses, to give your character a higher or lower charisma than absolutely nessecary, is because you might like to roleplay a little and make the charisma a reflection of the character's leadership and charm as you see it.

so "high charisma" is not a must right? with a charisma 13 or 14 everything can be fine..

I always choose CHR of 18 for RP purposes - I think you get a discount from merchants if you have a very high CHR (but I'm not sure)

I found several differences in CHR. levels. Bit of a spoiler here
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In the area directly north of the Gnoll stronghold in the southern region there is a bridge crossing the river. A man says that if you kill the bear chasing him he'll "give you anything". When I did it whith Chr. 17 I got the Boots of the North, when I did it with a lower CHR. I got about 40gp.

My cha is 16, where I can find charisma boosting items, tomes etc?

one more question, for INT and WIS 9-10 is enough for a fighter right? do they effect like cha?

Algernon's Cloak in a CHR-boosting item. It also has a practically inexhaustible supply of charm spells.

I don't think intellegence has any affect for a fighter but I think I read in the manuel that wisdom affects your saving throws/ I completely drained my intellegence on my fighter and used it for wisdom

I checked about the wisdom and it is only for spells that affect the mind and you would only want intellegence for lore.A 7 wisdom has a
-1 affect on mind spells but you need a whole 15 just to get a +1 bonus so there is a lot to work with.