When I started studying Arabic, I made a point early on of typing in Arabic. Then, most of the lessons were in English, but frequently used some Arabic vocabulary. And so at first I only learned to type those words in Arabic, and it was slow going, having to shift back and forth between keyboards, frequently having to check the keyboard location of some letters. But I was persistent.
I labeled the keys on my keyboard with a permanent marker (black keys, silver marker) and kept a "key" of their locations on my screen whenever I would be typing in Arabic--basically a list showing which English character corresponded with an Arabic character, laid out like a keyboard. I used it for a couple weeks before not really needing it beyond the addition of harakaat, and now I don't need it at all.
And the characters I drew on my keyboard have long since rubbed off. Because I started early, I was already typing away in Arabic while many of my peers were just ordering stickers to put on their keyboards to help.
But the more frequently I would type in Arabic, the more I began to notice a peculiar problem. On the occasions when I would like to type an Arabic word in flowing English and with Roman characters, I would find myself automatically striking the keys corresponding to the Arabic spelling. For instance, in trying to type out the word استعانة by spelling it as "isti'aanah" I would actually reflexively type "hsjuhkm" and keep going. In fact, it takes me at least two or three times longer to type the transliterated word than to type it in Arabic, because I have to stop and sometimes even (gasp!) look at the keyboard to check the English letters! And without surprise, I have a similar problem transliterating into Arabic, (eg, New York becomes نيو يورك,) albeit the difference is less pronounced since my Arabic typing is still slower than my English typing.
So I can type in English fine and in Arabic well but when I try to mix the two my brain has a really hard time coping with the transformation, and transliterating becomes a real difficulty, trying to make what are letters in one language correspond to sounds in another. It gets easier if I am able to see or look at a word already transliterated--then I can easily find the correct characters to represent it. But the first time writing it, I frequently end up with a weird jumble of letters that don't make sense either way, and have to slow down and think it through before I can type it. Has anyone else had a similar problem?