Web Application Internationalization, do it server-side or client-side?

Question

We are looking to internationalize a web application. Is it best to output translation Server-side (it is written in .net 4 C#) or Client-side (Javascript)?

We have already begun carrying this out Client-side by creating a JS file which contains a single object containing English phrases as the Keys (so developers understand what each message means in context), with values that are the string which is shown to the client for any alerts and prompts. We are thinking of extending this to all wording throughout the front-end.

Is this a good idea or is it best to carry out this kind of work server-side?

Update: Incase it helps to sway the argument, we don't use server-side controls heavily in our web application, the majority of our controls are jQuery/JS based.

Update: This particular application is not publicly visible (apart from the login page) so SEO concerns are not applicable.

Answer 1

SEO wise, I would recommend to do it server side and make the application available under a seperate url.

for example:

www.application/en/

www.application/es/ ...

Answer 2

The first rule of I18n: follow the standard way. Do not re-invent the wheel. In case of Asp.Net that means server-side Internationalization.

Well, sort of. If you happen to have tons of dynamically created controls, you still need some Localization mechanism for client-side scripts. You can centralize it, ie create one global array of translated strings and the model+controller, so you can ie populate it via AJAX call (although X would be best replaced by J for JSON...).
Anyway, your model should simply retrieve appropriate strings from resource files and controller should feed the JSON to the client side (good idea is to actually request smaller chunks, ie just the translation for given view/screen instead of translations for the whole application).

As you can see, the best would be some mixed approach. For many reasons, one would be it is better to use one Localization model for the whole application, ie use only *.resx files.
Besides, there is much more to Internationalization than just plain string externalization...

Answer 3

If you are showing only static content to user then go by client side internationalization. and if you showing content/messages those are dynamic, you should use server-side. but how are you detecting user locale?