Comment by int_19h

In Old English it was already pronounced /j/ there, even though the spelling was still "weg". Ditto for Old Frisian, so Normans had nothing to do with it.

The process is actually fairly straightforward. First you start with a common language that has two allophones for /g/ which are ~ [g] and [ɣ], depending on context; in this case, "weg" was [weɣ].

In Old Dutch [ɣ] then becomes subject to final obstruent devoicing, giving [x] of the modern Dutch pronunciation of the same word.

Meanwhile in Old English /k/ and /g/ (in either of its incarnations) palatalized in various environments instead. For [ɣ] in particular, it became palatalized after [e] in most cases - thus we get [weʝ]. And then [ʝ] is already very similar to [j], and gradually evolved into the latter. This all has already happened by the time most Old English texts were written.