I don't think there's one place that's generally agreed upon. A lot will depend on the type of language and on the source. Quite a few are invented by university students, and generally published in that student's thesis, dissertation, etc. Many companies have some sort of technical journal or other to publish their researchers' results. If it's somebody doing it on their own time, they might well publish it on their blog. If they decide to make the implementation an open source project, they might well publish it someplace like BitBucket, SourceForge, Github, etc. If it's (for example) a functional language, they might publish it someplace like Lambda the Ultimate. In some cases, it'll fit more than one category, and be published several of those places at once.