Instructions as a text manual (html pages likely) is generally a bad idea. Unless your app is extremely complicated/technical. But I'm not sure many users will read it.
What works well and is quite easy to localize:
1. Quick start with 3-4 screens explaining what the app does. This is actually the best way to get users interested in your app. Many people download popular apps and delete them less than 2 minutes after installation.
2. Onboarding for each screen which can be done with tooltips or highlights.
To see what I mean, download Packr on the app store: https://getpackr.io
The first screen is a quick start
Then add a new trip to see the highlights / tooltips.
If you already downloaded Packr, tap the menu and select "Hints", this will reset all onboarding and tooltips.
Second solution which has lot more text and would take ages to localize is to have a tutorial section such as Snapseed: https://itunes.apple.com/fr/app/snapseed/id439438619?mt=8