This is a very good question, but one that is surprisingly difficult to answer as no one really knows the size of this industry and companies are often reluctant to share their data because it is closely tied to global strategies.

In addition, the answer depends on whether one is interested in translation volume or strategic importance. The two differ substantially, and in important ways.

Let's start with translation volume, using figures from 2000 (the latest year for which I have reliable statistics). These figures represent the percentages (of those companies that are localizing at all) that are localizing into particular languages:

• English → French (~30%)
• English → German (~25%)
• English → Spanish (~25%)
• English → Japanese (~22%)
• English → Italian (~20%)
• English → Chinese (Simplified) (~15%)
• English → Portuguese (~12%)
• English → Swedish (~10%)
• English → Dutch (~8%)
• English → Korean (~7%)

Note that English is the source in each case. Despite trends toward "reverse" localization, localization is still primarily a vehicle from English to other languages.

These figures are a few years old, and the priority has shifted during the past few years away from European languages towards Asian languages, which leads us to the concept of "strategic" importance.

French, Italian, German and Spanish (a.k.a. FIGS) and other European languages are "maintenance" languages for many companies: i.e., companies already have a market in Europe, and have to maintain and serve it, but the market is not one that is seen as part of a strategic plan to gain global market share. This does not mean that these languages are unimportant, but rather that they are unlikely to represent new growth areas.

In contrast are "strategic" languages, i.e., those that represent new market areas with a potential for new revenue streams. In this view, China seems to be the number one language at present (I write this based on a number of LISA presentations and the general "buzz" in the industry).

While we don't have any hard data at present on strategic language (for obvious reasons, companies tend to keep strategic information quite close), if we look at those countries where U.S. and European businesses are trying to establish a foot-hold for consumer-oriented products and see new large markets (and where the market can be accessed easily with a single language), you will have a picture of the strategic languages. I suspect that the list would look something like the following:

• Chinese
• Japanese
• Spanish (for U.S.-based companies that see Latin America as a market)

While India is rising in importance, it isn't a major localization target yet because (1) it is fairly well served with English, at least for the most affluent sectors, and (2) for those not served by English, the picture is of immense linguistic fragmentation, with hundreds of languages that could be considered part of the localization picture.

In conclusion, the most important language question does not have an easy answer, but there are some general trends we can identify.