The binary language of vaporators is different from Binary, the language of droids Binary is specific a language , sometimes called droidspeak , Astromech droids such as R2-D2 communicate through an information-dense language of beeps and whistles known as Binary.
It is not "binary" as we use it (having to do with the digits 0 and 1).
While the language was common to all astromech droids , it apparently wasn't standardized in all other droids since we know that binary loadlifters required programming: "Vaporators!
Sir, my first job was programming binary loadlifters – very similar to your vaporators in most respects.
" ―C-3PO
It appears the vaporators Lars has are not able to communicate in standard droid binary language, and use a specialized "binary language of vaporators."
It's also possible newer machines have adopted the binary language, but these are simply salvaged or very old models that don't have that capacity and require specialized translation.
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In our world, there are many, many programming languages .
Not every computerized system can be programmed in every language.
Many can only be programmed in one, specialized language.
It seems like the Star Wars universe hasn't found a solution for this interoperability problem either.
Apparently the moisture vaporators are programmed in a binary code which isn't exactly the Star Wars equivalent of Java but rather something unique and proprietary.
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This scene is a little longer in the novelization: "I need,"
[Owen Lars] broke in, demonstrating imperious disregard for Threepio's as yet unenumerated secondary functions, "a 'droid that knows something about the binary language of independently programmable moisture vaporators." "Vaporators!
We are both in luck," Threepio countered.
"My first post-primary 1 assignment was in programming binary load lifters.
Very similar in construction and memory-function to your vaporators.
Star Wars Chapter 3
Although Threepio is bargaining for his life, meaning we have take everything he says with a grain of salt, his specific reference to memory-function suggests that moisture vaporators and load lifters accept different instructions than other sorts of droids.
1
Would that then be his second assignment?
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I imagined it as a sort-of API, like it has added functions to more finely tune calibrations.
For instance the binary language of most droids would include "wet", but a moisture vaporator would need to be far more precise, and may use special nomenclensure, if for instance, there are other gases being tracked, etc.
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On the planet earth, today, there are a huge number of binary encoding standards.
Based on 6, 8, 16, 32 or 64 bit groupings Encodings for specific character sets (for differnet languages), there are encodings which carry simple lean data (such as the readout from a scale) to more complex, video, photo and audio encodings.
Different manufacturers (for instance, Microsoft Office keeps changing it's file encoding to avoid their files being read by other manufacturers' software).
If, in the real world, we can't come up with a single standard for everything.
How would a galaxy of many worlds, a huge number of species who presumably each have distinct thought-patterns, with many languages and manufacturers, come up with a single standard binary encoding?
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The binary language and the machine language are synonyms.
Different machines need different languages.
At the lowest level, this is the arbitrary decision of how to assemble groups of binary digits into instructions.
At the higher level, it would be what peripherals are attached and what kind of interface is needed to talk to them.
If you want to think of binary as an actual language, there are numerous parallels with human languages, for example breaking words into phonemes, how many symbols are in the alphabet, what the grammar is and so on.
As to why moisture evaporators should require an non-standard language, there could be numerous reasons, optimisations to maximise compatibility with solar panel technology, maximising battery life, providing reliable unattended operation for long periods, etc.
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It's possible Owen was simply working off of C-3PO's list of talents.
3PO was explaining how he could speak a wide variety of languages; this is of little use to Owen.
The only skill that he needs a droid to know is the one that makes them a good moisture farmer.
And that's what he tells 3PO: you can be the best droid for talking to organics, but if you can't get my machines to work
you're no use to me.
The reference to binary language is simply used as a segue from 3PO's language skill and the desired skill of the operation of moisture vaporators.
It's also worth mentioning that droids aren't always going to be naturally good at talking to other machines, just like humans aren't very good at talking to monkeys.
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In  Star Wars: Episode IV A New Hope  Owen Lars says,   "What I really need is a droid that understands the binary language of moisture vaporators."   Was he just being overly specific in what he needed? (e.g., "I need a hammer for 3/4-inch nails")
Why would the binary language of moisture vaporators be that different from the binary language of other machines or droids?
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<star-wars><languages><droids>
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scifi.stackexchange.com/users/28571/Robert Soupe
Different machines need different languages, and it appears the vaporators Lars has are not able to communicate in standard droid binary language, and use a specialized, unique  "binary language of vaporators." While the language was common to all  astromech droids , it apparently wasn't standardized in all other droids since we know that  binary loadlifters  required programming. It is said that the vaporators are specialised and rather unique and proprietary in nature and are not capable of being pre-programmed. They function based on instructions that are different to other machines and droids using a specialised binary language. The reason Owen describes them using such language is also to impress C-3PO. 
Vaporators have a unique binary code. They require different instructions from other droids and machines. They are not pre-programmed as a consequence. They are unique, specialised and proprietary.  Owen uses such language not only because it relates to the way moisture vaporators specifically function but also because it’s the language C-3PO would have used.