Emoji search in non-iMessage apps I have English and emoji keyboards enabled.

In iMessage, I can just type "serbia" and I get the emoji for the Serbian flag.  However, in Signal, when I type Serbia, I just get Serbia and Serbian as suggestions.  I have another friend using the Signal app on iOS who does get emoji recommendations from his keyboard, so I have seen that it is possible, but all my recommended auto-replacements are textual.  I don't understand why this is different on my iPhone X and his iPhone 7.

It's very annoying to have to scroll through all the emojis and pick one rather than just type a word and get it.

What is happening and how do I fix it?
Bafflingly, this was the answer:

https://www.idownloadblog.com/2017/11/15/how-to-fix-predictive-emoji-not-working-iphone-ipad/

Apparently, the algorithm for recommendation for emoji replacement is per-app, which makes sense in that you speak differently in email than you do on twitter, but apparently, if you've never spun a random string of emojis together in a new app, the keyboard has to learn it from 0.  

So to fix this problem is: open your regular keyboard in the app of interest and type some words, then open your emoji keyboard and type a ton of random emojis (not even necessarily the one you want!). After you do, the recommendations will recognize that you mix English and Emoji and recommend them together, even from your English keyboard.  They will appear on the right hand side recommendation just where they do in iMessage.

(The link used Angola, not Serbia.)