front end - How do I create annotations for functions?

In 10.3, Mathematica starts captioning symbol-names into foreign languages if your Interface preferences are set to have Mathematica in a foreign language.

I poked around the Attributes, and viewed the Cell expression, but from the code I couldn't find any sign that this was happening at all (though it's obviously happening somehow).

I want to be able to make this happen on my own functions: to be able to supply translations, for instance, or extremely short inline explanations. For example, if I made a little function toInt, I might want to attach a type annotation String->Integer. This could help offset the verbosity of Mathematica code by making the notebook interface that little bit more intelligent.

One can see the translations available using WolframLanguageData:

WolframLanguageData[Graph][
 EntityProperty["WolframLanguageSymbol", "Translations"]
]

How does Mathematica do the translation annotations, and how can I do it myself?

Answer

Karsten 7. suggested a better method in the comments, which does not require a modification of any system files and can be used under English language setting. It works on my 10.2 installation after applying the following procedures:

1. 
   

   Under the user's directory (FileNameJoin[{$UserBaseDirectory,"SystemFiles\\FrontEnd\\SystemResources\\FunctionalFrequency"}]), add a file named, say, CustomAnnotation.m.

   
   


2. 
   

   Edit this CustomAnnotation.m as you want, consisting with the format of the built-in language specification file as described in my old answer (see below).

   
   


3. 
   

   Either open the Option Inspector and add the following path to Global Options ► File Locations ► PrivatePaths ► "TranslationData":

   
   

   
   
   

   FrontEnd`FileName[{$UserBaseDirectory, "SystemFiles", "FrontEnd", "SystemResources", "FunctionalFrequency"}]
   

   
   

   or execute the following code within the notebook:

   
   

   CurrentValue[$FrontEnd, {PrivatePaths, "TranslationData"}] = 
    Append[CurrentValue[$FrontEnd, {PrivatePaths, "TranslationData"}], 
      FrontEnd`FileName[{$UserBaseDirectory, "SystemFiles", "FrontEnd", 
        "SystemResources", "FunctionalFrequency"}]];
   



4. 
   

   Restart Mathematica.

   
   
   


5. 
   

   Execute the following code in Mathematica (replace $FrontEnd with $FrontEndSession for non-persistent modification):

   
   

   SetOptions[$FrontEnd, TranslationOptions -> {"Enabled" -> True, 
                                                "Language" -> "CustomAnnotation"}]
   

---

NOTE:

1. The following method works on my Mathematica 10.2, but not tested on other versions. [Also tested on Mathematica 10.3, Mac OS 10.11.1.]


2. The following method involving modification of a system file, thus is likely prohibited by the EULA.

---

1. 
   

   First find the language specific file located on a path similar to the following (I will use the simplified Chinese as a demonstration):

   
   

   
   

   C:\Program Files\Wolfram Research\Mathematica\10.2\SystemFiles\FrontEnd\SystemResources\FunctionalFrequency\ChineseSimplified.m

   
   
   

   
   


2. 
   

   Add a new function annotation line (the 3rd line in the snapshot):

   
   

   

   
   


3. 
   

   Open Mathematica with language setting to simplified Chinese, type ThisIsATestFunction in a notebook: