Weblate VS django-parler

For translations I can recommend you to use sites such as Crowdin, OneSky, Transifex, Weblate. Lot of smaller (singe or small team) developers are handling translations with the help of their users. You would be surprised how easy and how fast it is to manage translations at no (or nearly) cost this way. There is a lot of users willing to help to translate the app to their native languages.

weblate.org — It's free for libre projects up to 10,000 string source for the free tier, and Unlimited Self-hosted on-premises.

WebLate (their projects dashboard)

I'm using weblate.org. It's open source so it made the most sense to me to use for an open source Android app. It can also be used for free. It's not trivial to use but can be managed.

if the author of the app use a public translation service like https://weblate.org/ or https://crowdin.com/ you can do it via web browser.

For translation, using a Weblate instance makes a lot more sense over using Google Sheets https://github.com/WeblateOrg/weblate

hosted.weblate.org is only free for open-source projects, but it shouldn't be hard to find alternative hosting, or launch a Docker container in the cloud??

If there is not any, i can recommend Weblate, which is open source translation platform and hosting is free on their side for open source projects, or you can also self-host it.

I18n only handles static content and urls. If you need to have translatable Django models you should take a look at django-parler.

django-parler uses a different table for the translated objects and creates a new row for every language version of an object and connects them via foreign key and a join which should scale better imho. But it has the downside that it doesn't do a fallback on a per-field basis. So if a model has two translatable fields and only one has some content in the specific language, an object in this language gets created and the other field is empty and does not gets populated with the content from the fallback language (see this issue)