Constructed Languages
It should be obvious that creating a language requires some understanding of how languages work in the first place. This doesn't require knowing a lot of languages (although it helps) so much as it just requires an understanding of the technical and cultural stuff that forms language. If you want to learn it the same way I learned it, do the following:
1. Read some introductory works.
- For Phonetics: "Vowels and consonants" - Peter Ladefoged
- For Typology: "Introduction to Linguistic Typology" by Viveka Velupillai
- For Phonology: "Phonology: a cognitive grammar introduction" by Geoffrey S. Nathan.
All these are great at giving you a thorough but pedagogical introduction to the kinds of stuff that goes into making a language. Ladefoged tells you how to make the different sounds, Velupillai describes the overall tendencies and structures that tie languages together, how common they are, as well as giving examples of the inevitable exceptions. I haven't actually read "Phonology" though, but from what I gather it's a staple at the university, so it must give a fairly good look into how sounds are used in language.
You should be able to find them at the library or on the internet; that's what I did.
2. TAKE NOTES. Seriously. It will make it so much easier to remember all this weird shit, it's also much easier to find stuff in your notes than having to read the books all over again.
The main reason to do all this is that if you understand the underlying structures of languages. You're that much more likely to dodge the tired old trope of "It's English but with all the sounds scrambled around! And there's also some Japanese in there, too!". You're also less likely to accidentally create ugly ass meme languages or Tolkien clones. It also helps you in case you actually DO want to create a meme-language. The guy who made the Na'vi language for Avatar intentionally broke a lot of typographical rules.
3. Browse Wikipedia. It might be every academic's worst friend and best enemy, but this stupid self-contradicting mess of a website will help you very, very far on your way. Wikipedia might be dubious at times when it comes to details, but the important thing to remember is that you're not doing this as an academic, but as a creator. Whether the Pre-stopped Nasals and Pre-nasalised stops of Arrernte have underlying consonant clusters or if they're singular phonemes is not particularly important in regards to what you're doing. The fact that they have them is what matters to you. Even the most barebones language page on wikipedia tends to have a fairly accurate phoneme inventory, as well as listing the different allophones they have. So pick a language (any language) and take a peek. Now try going to the top and looking at the rest of the language family. Compare them. Try comparing them to languages from other language families in their vicinity. Wikipedia is a hobbyists best friend, as long as you take it with a grain of salt. If you come across something that lacks details, seems interesting, or feels dubious; try googling it. A lot of academic papers are free and available on the net.
Recommended pages and articles
Some different language families
https://en.wikipedia.org/wiki/Northwest_Caucasian_languages
https://en.wikipedia.org/wiki/Salishan_languages
https://en.wikipedia.org/wiki/Celtic_languages
https://en.wikipedia.org/wiki/Mongolic_languages
https://en.wikipedia.org/wiki/Iroquoian_languages
https://en.wikipedia.org/wiki/Maya_languages
https://en.wikipedia.org/wiki/Kra%E2%80%93Dai_languages
Very different languages
https://en.wikipedia.org/wiki/Polish_language
https://en.wikipedia.org/wiki/Luganda
https://en.wikipedia.org/wiki/Danish_language
https://en.wikipedia.org/wiki/Amharic
https://en.wikipedia.org/wiki/Greenlandic_language
https://en.wikipedia.org/wiki/Haida_language
https://en.wikipedia.org/wiki/Warlpiri_language
https://en.wikipedia.org/wiki/Javanese_language
https://en.wikipedia.org/wiki/Naija_language
https://en.wikipedia.org/wiki/Guarani_language
Meme-languages, because some languages are just weirder than others, and weird languages are always fun.
https://en.wikipedia.org/wiki/Ubykh_language (84 consonants and 2 vowels)
https://en.wikipedia.org/wiki/Nuxalk_language (Can form words with no vowels or sonorants)
https://en.wikipedia.org/wiki/Shilha_language (same as the above)
https://en.wikipedia.org/wiki/Moloko_language (between one and two phonemic vowels, look at the link in "Further reading" for more)
https://en.wikipedia.org/wiki/Yele_language (Coarticulated consonants, pre-nasalisation, post-nasalisation, labialisation, palatization and labio-palatization all come together to form one of the most ridicolous sound inventories on the face of the earth. Also a fuckload of weird spatial words. SIL has an in-depth description of the language)
https://en.wikipedia.org/wiki/Rotokas_language (The central dialect has the smallest known sound inventory in the world, also it completely lacks any nasals, tones or prosody related stuff whatsoever).
https://en.wikipedia.org/wiki/Taa_language (Also known as "The language that broke the IPA". Largest phoneme inventory in the world. Has dozens of different click-sounds, weird fucking consonants and an even weirder vowel inventory. If you want to create a really weirdly sounding language, use this as your base).
https://en.wikipedia.org/wiki/Tsez_language (Between 64 and 252 cases)
https://en.wikipedia.org/wiki/Pirah%C3%A3_language (Probably the single most controversial language ever. Apparently can't form embedded clauses at all. Also claimed to have the smallest phoneme inventory in the world, although you really have to stretch the definition of 'phoneme' to make that claim)
https://en.wikipedia.org/wiki/Arrernte_language (Everybody agrees that there's something weird going on with this language, but nobody can quite figure out what.)
https://en.wikipedia.org/wiki/Archi_language (I don't even know where to begin, it's fucking retarded and I love it.)
And the last batch of stuff
http://archive.phonetics.ucla.edu/main2.htm (Listen to different languages with phonemic annotations)
https://www.youtube.com/channel/UCo8b-uS6uD5l9YitDJpA2RA (A missionary channel that has recordings of Bible stories in a vast array of languages. Some of which are otherwise difficult to find quality recordings of, including Rotokas and Yele.)
https://www.youtube.com/user/WikiTongues (Find a qt and listen to her speak an exotic language!)
https://www.firstvoices.com/ (recordings of different Native American languages)