Origins/Classification

• Languages & Origins in Europe: Historical linguistics with prehistoric archaeology
• History and classification of Celtic languages (FFA thread)
• Omniglot: Guide to Writing Systems and Languages of the World
• Geographically accurate names

Grammar

• Notre Dame's Latin Dictionary and Grammar Aid
• Nifty Greek Handouts
• The Eton Greek Project
• A Gallo-Brittonic Grammar
• Welsh: dysgu-cymraeg and Say Something in Welsh
• Gender and formality in Polish grammar (FFA thread)

Dialects

• Map of North American English Dialects, Based on Pronunciation Patterns
• Sound comparisons for different varieties of English
• International Dialects of English Archive
• Speech Accent Archive

Slang

• Dirty talk through history
• William Shakespeare's Sexual Language: a Glossary
• Dictionary of the Vulgar Tongue: A Dictionary of the Slang of the British Underworld (1811)
• Dictionary of Victorian London
• Two papers on use of language in the HBO series Deadwood: “//Deadwood// and the English Language” and “Profanity Politics of the HBO's Series //Deadwood//: Authenticity, Lawlessness, and Living Outside Civil Society”
• Passing English of the Victorian Era: A Dictionary of Heterodox English, Slang and Phrase (1909)
• Old West Slang
• Jazz Age Slang
• Drunktionary
• British slang/sayings dictionary
• On the finer points of English swearing
• The Origins and Common Usage of British Swear-words
• Gendered curses for men in various languages (FFA thread)

Personal Names

• Behind The Name
• Kate Monk's Onomastikon (Dictionary of Names)
• Names from all around the world, sorted by region
• HearNames: Pronunciations of various names
• Naming customs in your country (FFA thread)
• Roman naming conventions
• Phoenician names
• Celtic Personal Names of Roman Britain
• Welsh names (FFA thread)
• Old English Names
• Byzantine names
• A Small Collection of Medieval Onomastic Articles by Sara L. Uckelman (it's actually not that small)
• Medieval Names Archive
• 14th-century Persian male names (FFA thread)
• Danish 19th-century upper-class names (FFA thread)
• Early 20th-c. male French names (FFA thread)
• Anglo-Catholic aristocratic naming conventions: see Recusant Families; Howard Family
• Source for absurd, yet very English names (FFA thread)
• French family names
• The American Name Society: Related Web Links
• A Guide to Names and Naming Practices, published March 2006 by the United Kingdom/Interpol.
• Meanings of some common Swedish name-elements (FFA thread)
• German names (FFA thread)
• Swedish soldier names
• Swedish //tilltalsnamn//
• None of your freaking movies get it right: A guide to Russian names
• Picking a Slavic-sounding name for a male character (FFA thread)
• Female equivalent of the Russian name Sergei (FFA thread)
• Polish nicknames (FFA thread)
• Chinese naming conventions
• Japanese names that are also names in other cultures (FFA thread)
• Naming conventions in your culture (FFA thread)
• Renren.com — Chinese equivalent of Facebook. If a name exists in its system, you can get an idea of whether it's considered male or female.
• International Naming Conventions (FFA thread): Scottish, Norwegian, Chinese, Finnish. More here on Norwegian naming traditions.
• Fantasy Name Generator
• FFA threads on naming characters: one, two
• Cracked post about naming characters
• Occupational names connected to the leather industry
• Naming Schemes
• Surname Database

Endearments, Diminutives, and Nicknames

• Russian nicknames for “Dmitri”
• Russian diminutives
• German endearments
• French endearments
• Portuguese nicknames
• Czech romantic endearments
• Lithuanian diminutives and endearments: Lituanus.org; FFA thread

Honorifics, Titles, and Polite/Impolite Address

• Japanese honorifics (FFA thread). This comment may be particularly helpful.
• Noble titles (FFA thread)
• Feudal Lord/Handmaiden terminology (FFA thread)
• Honorifics in Japanese translations from other languages (FFA thread)
• Which Japanese first-person pronoun would your fave use? (FFA thread)
• "Kisama" (FFA thread)

Language Construction/Conlangs

• Larry Niven's guide to coming up with sci-fi words
• “Brithenig itself is a constructed Romance language based on the premise that the Latin spoken in Roman Britain did not die out but rather developed into a modern Romance language akin to Spanish and French.”
• Xenolinguistics
• Making convincing-looking constructed languages without too much work
• Building new languages in sf/f
• Ardalambion: A Comprehensive Resource on Tolkien's Many Constructed Languages
• The Language Construction Kit
• “Fellow conlang nonnies, do you ever wind up putting in phonetic/phonological features that you have a hard time perceiving or reproducing yourself?” (FFA thread)
• Coming up with styles of address for a setting (FFA thread)
• "Anyone working on a conlang? Share a translation?" (FFA thread)
• "How do I strike a balance between ‘obviously alien’ and ‘unreadable’?" (FFA thread)
• "How realistic do you like your conlangs to be?" (FFA thread)
• Nonnies discuss having tried their hands at making conlangs (FFA thread)
• Nonnies discuss their conlangs (FFA thread)
• Short conlang thread (FFA thread)
• Languages, mostly conlangs (FFA thread)

Miscellaneous

• Fangirl Japanese (FFA thread)
• English-language fandom vs. German-language fandom (FFA thread, with Spanish-language fandom in comments)
• Terminology for red hair (FFA thread)
• Polari: The forgotten secret language of gay men