How do apps display stored notifications as localised strings? - ios

Question

I'm trying to localise my app, and have noticed that apps like Twitter and Facebook immediately switch the language used in previous notifications stored on the server to match the devices language. How are they doing that?
For example is someone comments on a post so that the notifications is:
John commented "hi" on your post.
It's later translated into French if my device language is set to French.
Would they store a localised string such as:
%# commented %# on your post.
And then somehow reference that string in the notification along with the variables?

Answer 1

There are many localisation related tools out there, one is like Phraseapp. The way these tools work are fairly simply, and the localisation is mostly front end driven, not backend.
You define a key for some content, and the key could accept parameters as well. So in your example, it could look the following.
English: user_commented_message = %# commented %# on your post.
German: user_commented_message = %# Kommentierte %# auf Ihrem Beitrag.
Than you save this into your Localizable.strings, what is being shipped with your app binary.
Once the localisation is done, all you need to do is to create the right payload for your notification. In your example, it would be looking something like the following:
{
aps = {
alert = {
"loc-args" = (
"John",
"hi"
);
"loc-key" = "user_commented_message";
};
badge = 1;
sound = default;
};
}
As you can see, you pass 2 arguments in the loc-args sections, where you pretty much define, what should be display instead of %# in your key. The order of the arguments is important, they will replace the %# in the same order, as they are in loc-args sections.
In the loc-key section, you just pretty much define what key should be used from your Localizable.strings. From this on, the Notification Center will just display the notification based on the device language settings reading the content the localisation dictionary, the Twitter or Facebook server has nothing to do with it.
For further reading, i would recommend to take a look at the Apple notification programming guide.
EDIT
This post says you are not able to use body and loc-args at the same time. It is an exclusive EITHER ONE or the OTHER relationship.
If it is in your app, than simply just use localisation. Do not send hard coded language content or store hard coded language text on the server, always use every text content with the localisation keys. It is still front end driven, the server should only keep the localised keys, not the content itself.