Now that Seed scienceblogs are taking over the world, one language at a time, the overlords are asking: which language to conquer next? That's a poll which you should go and take. But my thoughts first:
Some languages have few or no science blogs. Others have many but are a a closed community, only reading/linking/blogrolling each other. Others may have many, but they barely know each other and are not a community (yet). Others, though they share the language, stick to each other along national lines without much cross-over. Others crave international audience and write some or all of their content in (semi-broken) English. Should Seed go next to a market that is most ripe for the picking, or the one where they can make the greatest impact?
We are here in the USA where Spanish is the #1 foreign language, it is the mother tongue for many citizen's, and if you look south, there is an entire neighboring continent full of Spanish-speaking people (and yes, a bunch of Portuguese language people as well, I know). From an American perspective, Spanish as the next language for scienceblogs is a no-brainer.
But, if you live in Europe, Spanish language is, let's say, the top of the second tier of languages, behind English, German, French, Russian and Italian. If you live in Eastern Asia, in Russia, in the Middle East or in Africa, your perception of what language is the most important will be different as well.
If I think of foreign-language blogs that linked to me over the years, I barely remember any Spanish-language blogs that did so. But I remember quite a few in Portuguese and Russian (OK, also in Slovenian and Serbian, but that is my own 'niche' in a sense, not reflecting any kind of reality). I know one French blog, half of the posts of which are written in English. Recently, the most science blogging I see outside of English and German is in Italian - they are hot about it and keep linking to me and e-mailing me, etc - I will be going to Trieste in April to talk to them, etc. so it appears to me that theirs is the fastest-rising, most excited science blogosphere that wants to get international recognition - they may be the best organized and most receptive if Seed wants to offer a deal. Who knows what Russians or Chinese or Japanese are doing and what they think?
So, to summarize....
If the target is the language spoken by most people in the world, regardless of their Internet access - pick Chinese.
If the target is the language used by most blogs in the world, regardless of the way they are used and if they have science content - pick Korean.
If the target is the language understood, at least superficially, by most Americans - pick Spanish.
If the target is the language understood, behind English and German, by most Europeans - pick French (but beware that Science! on blogue already exists - do scienceblogs want to compete or open new markets?)
If the target is the language in a different, non-Western part of the world that is chock-full of scientists and science bloggers not known outside their region - pick Russian.
If the target is the language that already has a thriving science blogging community that is craving international recognition and will be receptive to Sb advances the most - pick Italian.
Now go and vote and voice your own opinion.
Well, I understand all your reasoning, but I still pick Potuguese - there really is an active Portuguese language science blogosphere and Brazil is one of the largest countries in the world and the second largest population in the Americas. Everybody knows how much of the world problems depends on the "scientification" of Brazilian people: the Amazon rain forest is here, we have good technologies on the production of bio-fuels, we have very deep soils with an incredible potential to sequester atmospheric carbon dioxide. What we don't have but need desperately is effective science education and popularization.
Just for you, I blogged on circadian rhythms. All I had to offer was a twenty-or-more year old experiment badly remembered from highschool by my husband, however, so too bad you can't read it and tell us if there have been any corroborating experiments.