Thanks for pointing this out, we will update the Loco translate tutorial.
1) The translation files should be present in the wp-content/languages folder.
The theme translation files is saved in wp-content/languages/themes folder
and plugins translation files is saved in wp-content/languages/plugins folder.
Since the global languages folder is never updated so the translations are safe from update and you should resync the files before you translate any string.
2) Please refer:
https://wplms.io/support/knowledge-base/translate-using-loco-translate-plugin/
I know this tutorial is not up to date but still the translation process is same, you just have to find the string in wplms theme or the plugin from where it is coming and then translate the files and save changes.
3) You just have to go to settings->general->site language, and choose your language and save changes. Now many strings will be automatically translated and if not then you can translate it using the loco translate plugin.
Let me know if this helps.