Hallowtongue

Hallowtongue is the dominant language within the isolationist community of Hallowside and the official language of the Halloric faith. The language is a mixture of D'Nalsian Common and Terran Primordial, as both languages were dominant in the region at the time when Hallowside was founded. The two languages continued to be the primary languages of the community up until the rise of Vaermosse Oridove, the religious extremist who transformed the community into an isolationist cult. As part of his rise to power, Ordiove utilized the adoption of Hallowtongue as a litmus test for those truly "worthy" of being a part of the community. Those unwilling to adopt the new language were banished from the community, and those who refused banishment were imprisoned and executed.
The adoption of Hallowtongue was seen as many to be a sign of defiance against a growing countermovement to Oridove's rise, as the language created an artifical language barrier between the leaders of Hallowside and those from outside the city attempting to negotiate for peaceful relations. Despite being an amalgamation of two common languages, Hallowtongue itself is syntactically and linguistically different enough from either languages that it's extremely difficult for a speaker of both languages to understand, and virtually impossible for a speaker of only one. Hallowtongue, alongside other measures put in place by Oridove and his allies, ensured that any attempts at cooperation between Hallowside and the outside world would inevitably fail, further isolating the community.
Beyond Hallowside, very few people have gone through the effort of trying to understand Hallowtongue enough to achieve fluency. Most of them are members of the D'Nalsi Empire's diplomatic corps, as the leadership of the Empire continue to hold out hope that the people of Hallowside will one day agree to reopen peaceful discussions with the rest of the Empire.