就我所知，HYDRO_LANG 是可以用的。最近翻源码，发现这样的代码：

// packages/hydrojudge/scr/tasks.ts
this.stat.handle = new Date();
this.rid = this.request.rid.toString();
this.lang = this.request.lang;
this.code = { content: this.request.code };
this.data = this.request.data;
this.source = this.request.source;
this.meta = this.request.meta;
this.files = this.request.files;
this.input = this.request.input;
let tid = this.request.contest?.toString() || '';
if (tid === '000000000000000000000000') tid = '';
this.env = {
    HYDRO_DOMAIN: this.request.domainId.toString(),
    HYDRO_RECORD: this.rid,
    HYDRO_LANG: this.lang,
    HYDRO_USER: (this.request.uid || 0).toString(),
    HYDRO_CONTEST: tid,
};
this.next = this.session.getNext(this);
this.end = this.session.getEnd(this);
logger.info('Submission: %s/%s/%s', host, this.source, this.rid);
await this.doSubmission();

但是 HYDRO_DOMAIN、HYDRO_RECORD、HYDRO_USER 好像用不了，HYDRO_CONTEST 貌似有个 Issue 说过可以用。

求问真的是这样吗？