Where have you gotten the most link-building mileage for a niche consumer app?

I'm working on PrettyFluent (https://prettyfluent.app) — a language learning app aimed at expats, travelers, and nomads living abroad. The pitch is practical and situational conversation skills (think: surviving a conversation at a Japanese izakaya, not acing an exam.)

I've started mapping out places where a link to the app makes genuine sense (directories, niche communities, etc.) So far my list includes the obvious ones: ProductHunt, Crunchbase, AlternativeTo, Indie Hackers itself, expat forums, and a few language learning subreddits.

But I'm curious what's actually moved the needle for others building in a niche like this.

A few specific things I'd love input on:

• Directories that surprised you. Ones that actually sent traffic or improved DA, not just checkbox listings
• Niche communities. Where you found a genuinely receptive audience
• Guest post / editorial plays. Worth the time investment for a solo founder, or not?
• Is it worth hiring someone on fiverr or upwork? Most advice from LLMs seem to say no. But would love to hear from a human.
• Any gotchas. E.g places that look good on paper but are basically link farms at this point.

The audience overlap I'm targeting: people living abroad or traveling long-term who are motivated to learn the local language but don't have time for a structured course. If you've built something for expats, nomads, or travelers, I'd especially love to compare notes.