All of this is taken into account. The ideas I'm trying to produce have a very general concept behind them and no specifics incorporated. For example, there are a few human-type races that are only defined by the type of response they give and how they sound (Military, Religious, Devious, Philosophic). There is no other background to them and therefore they can be applied to many concepts of humanoid.
I have no idea what races your talking about, but most of the proposed freeorion races have a lot of background, and a detailed physiology, any race that's so vague as to be describable in two words (Devious Humanoids for example) would probobly get a quick rejection for being underdeveloped.
Alien races are the easy part and require a day of making strange noises in my sound booth and can again be applied to just about anything.
You need the right noises for the right bizarre aliens. Something that fits their physiology and culture. Take the AEIOU, the two choices (grasshopper or dolphin) were both chosen because I'm guessing they're realitively easy sounds to create with telekenesis, and they both have a chirpy happy sound that's appropriate for a race that on the whole is happy with their life. The Stonecarvers on the other hand have a voice box so they have a language much more like humans, but are paranoid enough to develop a language explicitly deisnged so you can't read anything about the speaker from the speech patterns. A far cry from random alien noises despite being giant amoebas and cyborg land dwelling nautiluses respectively.
On the other hand, I do not think that alien races should overpopulate the human-type races in the game. When I say this, I use the phrase "Human-type races" with the heaviest sci-fi feeling I can get (Think Star-Trek). When I think of an intergalactic race of insects (not saying that you've suggested this) using some of the technology advancements that are an essential and already incorporated part of this game, it starts to lose realism.
Firstly having a dozen humanoid races with an identical tech tree is hugely unrealistic, so that's not going to make any diffrence. And secondly we're ignoring realism left right and center if it makes a better game. Bizarre non-humanoid aliens are more interesting than a dozen humans with funny foreheads so throw them in
BTW, having lots of humanoid races is immensely unrealistic from an evolution point of view, easily as unrealistic as having dozens of bizarre aliens with identical tech.
The languages should reflect this and should not be to far off from the core of the game.
Given the significant variation in human languages I'd have no problem accepting massive differences in alien languages.
Strange and unconventional races can be used as NPC's easily, but including them as playable races would take away from some of the current game play systems that we have already built.
No. It wont.