Mixed Language on digest mail

We need a lot more information.

1. Is the Arab item the translation of the English one?
2. Are they both visible to the receiving user, as single nodes? in node lists?
3. What behavior do you expect and why?
4. I presume the default language of your site is English, right?
5. What is the user's preferred language?
6. What template language do you expect to get and why?

also the body summary is not taking the full width

Create a new issue if you want to pursue this. (I don't think Subs has any control over this.)

Some answers and more questions:

1. Is the Arab item the translation of the English one? yes

Subs currently has no notion of translation groups. This concept is D7 only and will go away in D8. It's unlikely that it will be implemented in Subs for D7, unless someone steps up and does all the work, that is. In other words, Subs sees the two nodes as two separate items that need to be sent.

2. Are they both visible to the receiving user, as single nodes? in node lists? yes

In that case I don't see how Subs could know which one to send and which one to ignore.

7. What is the content type of these nodes?

8. What kind of subscription are you using? by content type? by taxonomy? or what?

3. What behavior do you expect and why?
I expect that the user receive only the preferred language email , so when the user subscribe to a content , the language selected is stored in this subscription.

At this point the language is completely ignored at the time of subscribing.

I'm not sure it's legitimate to assume, just because the current node happens to be in Arab, that the user wants to get only Arab content. This may be different, depending on the kind of subscription.

For example, if he subscribes to an Arab term, then it may be the correct assumption. I don't know enough about multilingual sites, but I would assume that if the Arab node has an Arab term and the English one an English one, then subscribing to the Arab term would get you only the Arab node. So this would work as you expect.

And if he subscribe with two languages [...]

How would he do that?

[...], then he should receive separated mail for each language

You mean separate Arab and English digests? That doesn't make sense to me.

I would expect the template language to be chosen according to the user's language preference, but if this actually works (and it seems that it does), I see no reason not to put Arab and English items into the same digest (if the user chooses digest). In non-digest mode, I would still expect the template to be in the user's preferred language (a.k.a. the chosen UI interface language of the site), no matter what the language of the contained item is.

5. What is the user's preferred language?It depend on the language he select with language switcher

The language switcher? What module implements the language switcher? How could Subscriptions know what language that is? I would prefer to use the language that the user selects on his user/%/edit page.

6. What template language do you expect to get and why? separate language

I don't understand what you mean. Chinese? That would be a separate language...

9. Apparently, your site is set to use path prefixes (en/). Do you have this set to override the user's user/%/edit preference? When Subs runs during cron, it cannot know what prefix the user usually uses for accessing the site. In fact, the user may use different prefixes at different times. I'm confused about this...

10. You've picked an interesting example. Even the Arab node has an en/ prefix. Is that correct? Can the node be seen at that path? Does Subs always pick en/ because the site's default language is English?

Closing this as a duplicate of #1088560: Content translation subscriptions filtered by language preference.