The word angulus (angle or corner) looks like a diminutive. Was it derived from some other word or stem using the diminutive -ulus suffix, or is looking like a diminutive coincidental? It looks like it could be related to the verb angere, but I haven't found a related non-diminutive noun.
angulus is cognate with English “ankle” (and other Germanic words) and Russian “ugol” (corner) and its Slavic cognates, so the /l/ is Indo-European heritage, not a Latin innovation. PIE reconstructions such as *ang-(o)lo- or *h2eng-(o)lo- have been proposed.
angere “to strangle” is supposed to be from *h2emǵho-, with a palatal *ǵh.