Hi. I'm Italian. I am exercise TRAINING/TEACHING myself to speak English because it's fundamental in ESSENTIAL FOR my job.

My native language is Italian and I AM available to teach this language IT  to somebody ANYONE.
I don't speak HAVE NOT SPOKEN English since many FOR A LONG time and SO I must to exercise myself PRACTICE. I must reach a fluent LEVEL OF English speaking.

Hi. I'm Italian. I am exercise myself to must practise speaking English because it's important to my work.

My native language is Italian and I am available to teach this language to anybody.

I haven't spoken English for a long time and I must to practise exercise myself, i must to reach a fluent level in English speaking.

OK, just a few important grammar points:

I haven't spoken English... the only way to connect the past and the present properly is through the present perfect tense. You cannot use simple tenses here. That will not work.

Use since when you give a starting point in time (Since when? Since I left high school; since 1998), and for when you give a length of time (For how long? For eight years; for three weeks).

Must and other modal verbs (will, can, should, could, etc) are never followed by to.

Some reflexives are implied in the English verb, so no need to use -self. I exercise, I practise, I wash, I remember...

The end of your text needed a noun. Verbs with -ing added can function as either an adjective or a noun, so be careful. Rewrite if necessary.

Hope that all helps.

Hi. I'm Italian. I am exercise myself to speak practising my spoken english because it's fundamental in my job.

My native language is italian and i am available to teach this language to somebody.
I don't speak haven't spoken english since many time for a long time and i must to exercise myself practise, i must reach a fluent english speaking become more fluent.

:)