I could have sworn I saw you'd be able to properly merge one mercenary company with an army in this version...

[Pavía]

I would argue that adding an exception about mercs not merging with other mercs isn't a first/second/third language issue. The main problem with the wording was the mention of the specific exception. Mentioning such a specific exception when mercs don't merge in general doesn't make sense regardless of language. I'm guessing it is more a result of dev diaries being a rather low priority, and not necessarily something the people writing dev diaries enjoys (I doubt many devs became game developers because they wanted to write marketing pieces on their work). It's therefore not surprising that they end up being rushed, and possibly not being checked by other people with knowledge of the patch content.

With the below being the only dev response to the dev diary (ignoring BjornB's forum betrayal comment), it seems very likely that the dev diary is a case of being rushed:

Yeah, it isn't a case of a first/second/third language issue, neither is it a DD being rushed or not checked (we tried to be very, very careful with that one, as we wanted to be very clear with all the stuff presented on it, both for the DLC and for the free QoL features; so a lot of people reviewed it, and I reworked it a lot from the first draft). It's just a case of bad wording that went unnoticed under the radar, even with multiple different people checking it.

Sorry for the inconvenience regarding it, the intended behavior was already explained perfectly by @FrogCrusher .

PS: It's true that the last DDs were not so much a priority compared with the last preparations for the release of King of Kings the update 1.36, and the post-release support of 1.36; that's why I've been more active in answering threads like this checking for post-release issues, and I still have as a pending task to go answer the last DDs.