Noldorin and Sindarin. In both cases more by invention than involuntary. But after Rising of Sun change was sudden and swift - and the Noldor brought a special curse of changefulness with them (designed to cut them off from converse with Valinor?). The two tongues there changed and grew alike.
Generally in Beleriand a Noldorized (slightly) Sindarin was spoken.
In Doriath less Noldorin if any. [?Ossiriand] to be like Beleriandic.
The difference here from the primary text lies in a denial of any very significant difference between the language of Beleriand and the language of the incoming Noldor, with the subsequent history (as it appears, from the brief and hasty words) being rather one of the coalescence of the languages than of the abandonment of Noldorin.
The excursus on languages in GA 2, written in a much smaller script than that of the main body of the text, reads as follows.
It was indeed at the landing of Feanor three hundred and sixty-five long years of the Valar since the Noldor had passed over the Sea and left the Sindar behind. Now that time was in length well nigh as three thousand and five hundred years of the Sun. In such an age the tongues of Men that were far sundered would indeed change out of knowledge, save such as were written down in records of song and wisdom. But in Valinor in the days of the Trees change was little to be perceived, save that which came of will and design, while in Middle-earth under the Sleep of Yavanna the change of growth was slow also.
Nonetheless in Beleriand the Sleep before the coming of the Sun had been stirred (as elsewhere is told) and the language of the Sindar had in the long years changed much, even in unheeded growth, as a tree may imperceptibly change its shape: as much, maybe, as an unwritten tongue of the later days woud change in five hundred years or more. Whereas the Noldorin tongue, albeit still far nearer in most ways to the ancient common speech of the Eldar, had been altered by will (to forms that seemed to those in Aman more sweet upon the tongue or in the ear) and by the invention of many new words unknown to the Sindar. But speech between the two kindreds became easy and free in this wise. First that after the Rising of the Sun the change of all things in Arda was sudden and swift, and in the days of the Wars both the tongue of the Noldor and that of the Sindar changed greatly: moreover, whether by reason of the like clime, and soil, and the like fortunes, whether by intercourse and the mingling of the peoples, the two tongues changed in similar ways and drew together again. Secondly because in time it came to pass that most of the Noldor indeed forsook their own tongue in daily use and took the tongue of Beleriand instead, though they enriched it with many words of their own. Only in Gondolin, which was early peopled (by Noldor alone)(8) and cut off from intercourse with others, did the Noldorin tongue endure unto the end of the city; whereas in Doriath only was the Sindarin tongue maintained untouched by the Noldorin and less changed than the language of those without. Now this change in the speech of the Noldor came about in this wise. First: though the Sindar were not numerous they much outnumbered the hosts of Feanor and Fingolfin, such as survived their dreadful journey. Secondly: because of the mingling of the peoples, whereby in all the countries save only in Doriath though the princes of the Noldor were the kings their followers were largely Sindarin by race. Thirdly: because after the death of Feanor the overlordship of the Exiles passed to Fingolfin (save among the followers of Feanor's sons), and he acknowledged the high-kingship of Thingol, being indeed in awe of that king, mightiest of the Eldar save Feanor, and of Melian no less.
But Thingol, because of the grievance of the Teleri against the Noldor, would not speak the Noldorin tongue and forbade his subjects to do so. Moreover it came to pass that the Noldor, having of their own will