Hello.
This little story is not about what files and what you need to open to translate your favorite program, but about what accompanies the translation.
Since last year (2013) I have been involved in the localization of applications for OS X (and quite a bit for iOS). At first it was just a hobby, then I began to communicate with many developers and work with some of them. In the process of searching for those who are willing to cooperate, I faced various problems and received different answers. Most, as expected, are negative. About the reasons below. In general, now I would like to tell from personal experience what awaits those who want to do the translation themselves: for free or for a fee. So…
Applications for OS X and iOS appear daily. Popular and neglected, well-developed and "put together" in a hurry, useful and not very. They are different. They are extremely many. However, most Mac or iOS users already have their own list of favorite programs, which still need to earn a place. The application with the English interface in this list is a familiar affair. On the one hand, for many users this is not a problem: someone is well acquainted with English in principle, someone is used to working this way in the absence of an alternative, for some programs, translation is not needed because of their simplicity and clarity. On the other hand, localization always attracts new customers. I will not undertake to say what additional growth can give an additional language (given the fact that some users would have agreed to English), but, as one developer told me, adding a new localization is always justified. At least in terms of positioning your product. At a minimum, there is an opportunity to talk about your application to a new audience.
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Now regarding the very audience and the possible increase.
Once, in correspondence with one Danish developer, I learned about the Appannie service. One of its functions is to view the list of top applications in various stores. We are interested in the Mac App Store. So, we open the information about "bestsellers" for June 18, 2014 in Russia.

Free down, about this later. Among paid - pay attention to the number 3. This is Reeder 2, released recently. Now the program has only one language in its arsenal (I will not suggest ...). Would you like to see her in Russian? I would like to. I think I'm not alone in this desire. Reeder, of course, is not Xcode (if we talk about the complexity of the interface), but not a Bookreader, for example, in which everything can be done in two clicks. Therefore, each new language is not only a pleasant, but also a useful option for a certain part of users. Whether the developer’s plans include adding Russian (or at least some other) localization is not clear. To my letter with this question, sent a couple of days ago, there is no answer yet.
I believe that it will be negative. And now I will try to explain what I have reason to think so.
Further I will give the main concerns of the developers regarding the localization of applications.
1. Undervaluation of the market
Many of those to whom I wrote answered me that a targeted entry into the Russian market is unlikely to bring dividends. They say that localization costs will not pay off: few people buy a program in Russia, it is unlikely that Russian will significantly change something. Who wanted - buy in English. Not quite objectively, because in half of the cases the cost of the translation will not exceed 10 times the cost of the program in the App Store. But along with the translation of the program, a Russian description will appear in the store. And as 10 additional people such innovation, probably, somehow attract.
And then the argument number 2.
2. Further support?
Translate the program - this is not the end. In a couple of weeks, a caring developer will come up with and add some feature that requires translation. As I was told in several companies, they were faced with the fact that the former translator simply did not get in touch, and the program actually went out in an unfinished form. Someone is not particularly worried about this, but someone simply does not want to get involved with individual developers initially. And it works only with companies.
3. Lack of financial capacity
If the software developer is a very small company, or even one or two comrades, you can hear that it is simply not affordable for them now.
4. Why fooling?
These are those who reasonably (or not) believe that English is enough. The program is already clear, what is there to translate?
5. "We are not ready yet", "We plan to do this in the future"
Polite refusal. You are told: “We are, in principle, interested ... but it is still too early. We now have other priorities / a lot of other work / we plan to do localization later, "etc.
In the context of the last example, I will give the answer of a member of the Pixelmator Team to my proposal for cooperation:

Well, I have patience ...
By the way, the company Applingua Ltd, which made the translation for Pixelmator, successfully updated all localizations with the release of a new version of the program. Robert Lo Bue (I won’t distort the person’s name with the translation), the director of the company, continues to work with the Pixelmator Team, so my patience is further enhanced by the opportunity to reach developers through a Welsh company that actively attracts translators from different countries.
And again about the market. Throughout the story, I focused on applications for OS X, because worked with iOS less. So: one online mobile translation service estimates a Russian-speaking iOS audience at 33.4 million users.

It is hard for me to assess the objectivity of this data, but I suppose that proportional separation between languages ​​can be true. Russian - on the 5th place among the additional languages. But we hardly see Russian more often than German, French and other languages ​​that are lower in the list.
As a result, I have a question: why do I need to add some European language to the application, and leave the Russian audience with English? Or are we more often than others buying programs without native localization, or somehow they don’t appreciate us.
A few words about non-commercial localization
If you want to translate something “for the soul” (or simply the developer does not want to implement a Russian translation, and you still intend to do it), you can do the localization yourself. There are also 2 options here: do it all alone, using different programs like NibUnlocker and editing compiled files in a text editor, or ask the developer for non-compiled files to make the task easier n times. However, remember that you will not necessarily be helped. And even if they help, in the case of a program update, you will need to write to the developer again or still edit the compiled files. There really is enough enthusiasm.
Finally, let me give a few small tips to those who, like me, decide to do application localization.
1. Always write to the developer. First, he may be interested in your services. Secondly, even if he is not interested, he can help you. Be prepared for what everyone does not answer. In my experience, the answer comes from ~ 70% of developers, which, by the way, is also quite good. The main thing is not to be afraid to write: nobody will answer you rudely. On the contrary: thank for the offer, regardless of interest.
2. Be prepared for large volumes of work: you usually need to translate much more than it seems at first glance. There are always many menu items, tooltips, settings window, etc.
3. [
Main rule ] Say "NO!" To automatic translation. It is better then to leave the program alone and not to mock future users. The same Google Translator or Promt is useful for comparing, as well as for finding options for translating individual phrases, phrases. Do not be lazy to use the dictionary and word-for-word translation of Lingvo, to search for incomprehensible idioms on the Internet.
4. Keep track of line lengths. It's no secret that the English letter is quite compact. Compared with the Russian, so much smaller. Naturally, in some cases (description of functions, decoding errors in a separate window, tooltip), the size of the text is not important. But it is crucial for the signatures of most interface elements. If the text is too long, you will have to resize the adjacent element, other elements, the window. This will create additional difficulties and will still hurt you when updating the translation in the future.
5. Always check spelling. Depending on the program in which you work, errors in one or another language can be highlighted or not. Anyway, after completing the work, use text verification, for example, using Speller from Yandex. But just do not forget that in case you missed something in meaning (they simply missed the word), in 99% no service will tell you about it.
During my work in this area, I gained a unique experience, met many interesting people, earned ~ $ 600 and launched my website. I am sure that I did not waste my free time during these 6 months. I have no experience in software development, I don’t know enough about programming, and I don’t have great English, I guess But I like what I do, and I hope it works. This I mean, that doing business that brings pleasure is still worth it. The main thing to start.
Good luck with your projects!