I heard a great word today: tməhbəl تمهبل "behave like a crazy person", a verb derived by consonant extraction from the noun/adjective məhbul مهبول "crazy", itself a passive participle (of a form familiar from Fusha, with a prefix m- plus an infix) from the verb hbəl هبل "go crazy". A similar process, whose intermediate stages do not however survive in Darja, brought about tməsxər تمسخر "kid, joke"; cf. Fusha saxira سخر "mock, laugh at".
Regular diminutives are formed with an infixed i, optionally with a feminine ending added. In Dellys, nouns normally form them either by simple infixation or (for three-letter roots) infixation with an added y after the infix, but adjectives add an extra consonant after the i - either a copy of the second root consonant (eg kħiħəl كحيحل "a little black", from kħəl كحل "black"), or a w (ṣġiwəṛ صغيور "tiny" from ṣġiṛ صغير "small"). "One", unlike other numbers, agrees in gender with its referent, a property of adjectives; thus it is perhaps unsurprising to learn that it can take the adjective-style diminutive wħiħda "a little one."
The English "substrate" in my Darja shows through most clearly, I suspect, in noun agreement. Gender for inanimate objects has always given me trouble; the gender of a noun is almost always obvious from its form, yet if I don't concentrate I still tend to revert to some kind of default gender when the noun in question is unmentioned or is in a different sentence. Number is a lot easier; but even there there are a few points I need to focus on. For one thing, I tend to give words like səṛwal سروال "trousers", which take plural agreement in English, plural agreement when they should be singular. (I am not alone in this kind of error; talking to a friend born and raised in a largely Kabyle area of the Casbah in Algiers, I heard that in his neighbourhood they consistently say things like əlma bardin الما باردين "The water is cold (pl.)", because "water", aman, happens to take plural agreement in Kabyle.) But there is a large class of nouns in Arabic in general where the unmarked form is essentially a mass noun but is used in most contexts where English speakers use plurals, and the singular (or rather the singulative) is formed from it by adding a feminine marker. For example, if you want to say "I bought some figs today", or "I made some fig jelly", or "I see a fig tree", for any of these you would use the unmarked bəxsis بخسيس "figs"; for "I ate a fig" or "This fig is tasty", you would add the feminine ending to get bəxsisa بخسيسة; if you said something like "There are three figs on the table", where the figs are individuated but there's more than one of them, you would pluralise the singulative (feminine) form and say bəxsisat بخسيسات. So in most contexts, the English plural "figs" gets rendered by the mass noun bəxsis. The difficulty that arises is that, as a result, I tend to think of words like bəxsis as plural, and give them plural agreement, when in fact I should be giving them singular agreement like any other mass noun.