Make the language switching code more robust

[xfq]

Since language switching in ED has been unable to work for a few days now (see #231), I made a pull request to fix this issue first. I suggest that we merge it, and we can continue to improve the code in the future.

[himorin]

we may not have any additional code for check or debug in the future, but how about to add one function like below for ease of maintenance and modification.

// as replaceHeaders('editors', translations[lang].editors);
function replaceHeaders (target, translated) {
    if (document.getElementById(target)) {
        document.getElementById(target).textContent = translated;
    }
}

[himorin]

Ah, one point. Do we want to add a line for console log output, for telling us about error?

[xfq]

It is indeed a good suggestion. I just refactored the code.

I used console.log instead of console.error, because sometimes missing headers may not be considered errors (like previousversion).

[xfq]

Thanks for the review @himorin. I'll go ahead and merge this.

@r12a feel free to comment on #231 or submit a new issue/PR if you have any question/concern/suggestion about this.

[r12a]

@r12a feel free to comment on #231 or submit a new issue/PR if you have any question/concern/suggestion about this.

From a quick scan i don't notice anything problematic. (However, i would have preferred to keep the layout consistent, ie. no ; at line end, and } in line with block end (Python-like layout). That's only a minor thing though.)