Okay. I just read the article and watched the video and the article is rather misleading. It is, while a milder form, a misunderstanding of what Matt Cutts was saying. This happens often even by experts in the field. One needs to listen to what Matt says carefully and not read into what is said too much. Often, people hear what they want to hear and run with it. Matt needs to be taken rather literally. He prepares his statements carefully often in advance and very precisely.
The articles notion that "it just doesn't matter" is false. If you view Matt's video, he is clearly saying that it does matter and that the performance of sub-domains comes with a price if more than one sub-domain is used. The effect was left somewhat fuzzy by Matt.
Here is the "skinny" on sub-domains vs. sub-directories.
Sub-domains are often more work.
Sub-domains may be necessary to host different applications that may not live well within the same web space.
The traffic to a sub-domain (blog.example.com) may be harder to make transparent in operation to the parent site (example.com) and conversion may be more difficult though this can be overcome.
The traffic to a sub-domain ranks the sub-domain (blog.example.com) and positively effects the parent domain (example.com) less.
Sub-domains require more work to undo if it comes to that later down the road.
It is true that Google recognizes sub-domains as belonging to a parent domain. Google does look for relationships between sites.
It remains true that Google treats each sub-domain as a separate site and that site will perform independent from the parent site assuming that there are no trust issues with the parent site.
It is true that when a sub-domain performs well, it positively effects the performance of the parent site, however, this is limited and depends upon how well a sub-domain converts traffic from the sub-domain to the parent site and other factors.
Where as, if a sub-directory is used, the traffic and links benefit the domain name (example.com) completely.
Matt was saying that if multiple sub-domains are used and search results are found in each sub-domain, then it is harder for multiple sub-domains to gain a presence in the search engine results page (SERP). However, he was also indicating that there may be a tolerance for this. What tolerance exists, is not clear. I would assume that two sub-domains are okay. Matt's comments referred to a tactic of abusing sub-domains for a greater presence in the SERPs. I cannot see that your scenario would cross this line.
Where sub-domains are most beneficial are when the topic of the sub-domains are divergent from the parent domain and would dilute the search performance for the parent domain.
You have two choices:
Choice 1: Create two sub-domains one for each language and let each sub-domain and parent domain perform on their own which should (at least for the most part) work okay but may not benefit the parent domain much.
Choice 2: Create two sub-directories one for each language and fully benefit the parent domain from the traffic and links each language blog creates.
What I do not know.
Is how to have more than one language content on a site. This is done often and there are some (several) good answers here that can help, but I will let that be another question.
If I were given the choice:
I would opt for creating sub-directories rather than sub-domains if possible. Your site would perform best this way. However, it may be necessary or easier to create sub-domains for operational reasons. As well, each blogs performance can be measured independently from each other and the parent domain.
In the end:
It is a choice you have to make and I assume some experiments on how to make sub-domains vs. sub-directories may be necessary to see which is preferred at least operationally and then personally.