Originally in WFRP 4e, each career's first level had 8 skills. To complete the career, you needed at least 5 advances in all of them. Later, new careers were given 10 skill in their first levels, and to complete the career, you needed 5 advances in eight of them.
Hedge Witch was one of the original careers, so it had 8 skills. However, when Archives 3 was being made, the career got updated, gaining Secret Signs (Hedge) at level 1, with the book saying it lets hedge witches share information, and allows travelling hedge witches to spot local ones. However, during proofreading, it was pointed out that this only added up to 9 skills, and that a 10th would need to be added to bring it up to the new standard.
When the book released, it added not just Secret Signs (Hedge), but also Language (Belthani), retaining the same explanation. I think there's two ways to look at this. The first is that it was an off-the-cuff addition that doesn't make too much sense with the millennia-long domination of Reikspiel. The second is that, regardless of when or how the skill was added, it makes sense for a hinterland tradition of knowledge keepers to retain their traditional language and speak it as a second tongue.
The thing about the latter view is that it describes druids just as much as it does hedge witches, so how did the Cult of the Mother lose knowledge of even spoken Belthani so much more thoroughly than the Hedgewise did? I think the answer might be hinted at in WFRP 2e: Tome of Salvation page 7:
Most believe the Cult of the Mother died out long ago. They are wrong. Not only do the Great Families of my Order continue Her traditions, but the sickle is born by others, which most of whom hide far from prying eyes. [...] Indeed, a full third of the Druidic Families stubbornly spurned Teclis, refusing to believe his 'truth,' and fled into the dark forests, just like the prehistoric tribes of old. But those who remained, listened, and then eventually understood. Not long after, the Jade Order of Magic was formalised, and we were its numbers. We didn't change our beliefs -- indeed, we practise the Old Faith still -- but we understood them for what they were: a twisted reflection of the truth. Since then, our role as Nature's Guardians has brought us into contact with many others who believe they are the Children of the Belthani. They are all, I am quite sure, just as wrong as we were.
To begin with, it seems like the Cult of the Mother didn't think of themselves as Belthani, but rather as the Belthani's successors or descendents. The druids who rejected Teclis' teachings didn't "return to the dark forests they came from", they "fled to the dark forests like the ancient tribes did", implying that the Cult of the Mother were not hidden forest-dwellers before Teclis arrived. This is reinforced by saying that, now that Jade Wizards were forest dwellers, they were encountering a bunch of people who think they're the Belthani's successors/descendents.
Two thoughts come to me. First is that maybe the Cult of the Mother weren't direct inheritors of the Belthani's traditions. Might be that, in the millennia after the original Belthani druids' passing, rural folk looked at the oghams left behind, the stories of druids and ancient gods, the few Belthani phrases and songs they inherited, and the abundant Ghyran of the natural landscape and cobbled together a new druidic tradition, emulating what came before. Neo-druids basically. That's why they have such scant knowledge of the Belthani language where the Hedgewise, who actually do have an unbroken line of knowledge, can speak it fluently.
The other thought that comes to me is that the Cult of the Mother is conceited as all hell. Erowin is dripping condescension at every turn, even towards the forest druids the Jade Order newly encountered, who may very well be direct inheritors of the Belthani druids who fled into the forest, and we know from Panoramia's mum that they don't think men are suited to Ghyran at all.
Archives 3 p56 says "witch hunters and Jade Wizards have driven Old Faith druids into obscurity by claiming that their nature gods are truly Chaos daemons"*, which I originally found baffling given that jade wizards themselves were, and in many cases
are, Old Faith druids. However, with the context of Erowin's words, I think the Cult of the Mother may see itself as a domineering major cult, one that knows the truth of their faith (Ghyran/the Earth Mother is the only part of the Old Faith worth bothering with) and that they're owed superiority because of it, and that anything challenging that position is evil and needs to be suppressed.
*Context. This is in a one-paragraph section called Dark Druids, which says there were druids who had mortuary rituals, that they repurposed waystones into animal totems, and that some barrows are guarded by those totems. I think it's possible there was more written in the section that was cut for page space before it reached the proofreading stage. Also, earlier in the page, it said that there were jade wizards who are sympathetic to the Old Faith.
In conclusion, could be the Cult of the Mother
aren't direct inheritors of Belthani druidic traditions while the Hedgewise
are direct inheritors of Belthani Hedgewise traditions, which is why the Hedgewise speak Belthani way better than the Cult.
EDIT: Could be that direct inheritors of Belthani druidic traditions still exist and speak Belthani too, descended from the druids who fled into the forests, went to ground (like the Cult of Ahalt), or, if we're taking DPG's lore (which we aren't), took sanctuary in the dwarf kingdoms.
EDIT2: Winds of Magic page 78:
'We druids, who study the Lore of Life, know that [the Jade Wind] is the single most powerful and single most important wind. It is the one element that all living things must possess. It emerges from life just as it gives life; it is found in the blood of creatures, and in the sap of plants. It is the very stuff of life. [...]
– Tochter Grunfeld, Jade Wizard Lord
Not beating the 'conceited' allegations.
