Typesetters and printers.

Here the answer of "Oxford dictionaries" (other dictionaries could have a different policy): "How do you decide what to include in a dictionary? Much depends on the type and size of the dictionary being compiled. In the larger dictionaries the main criterion is how widely a word occurs: we never omit a word because we think it’s not ‘good English’. (If a word is used only in very informal contexts, or only by specific groups of people, or if it is offensive in some way, we make this clear in the dictionary entry.) In a dictionary such as the Concise Oxford English Dictionary, constraints on size mean that the usefulness of the words included has to be carefully considered. If a dictionary is written for children at the primary school level, some of the more ‘adult’ words are excluded. In compiling a dictionary of current English, it is likely that obscure and obsolete words would be omitted. In a huge dictionary such as the Oxford English Dictionary the aim is to be comprehensive, and all words, whether obsolete or current, are included. New words are only included if we find enough examples of their use in printed sources." Source and further information: http://www.askoxford.com/asktheexperts/faq/aboutdictionaries/include?view=uk "How do you decide if a new word should go in an Oxford dictionary? We conduct a Reading Programme to collect examples of words in use. If we have enough examples to show that a word has genuinely achieved currency, then we add it to our list of candidates for inclusion, and the editors research its usage and draft an entry. The general rule of thumb for the OED is that any word can be included which appears five times, in five different printed sources, over a period of five years. Oxford's smaller dictionaries of current English may include words with a shorter history. Once a word has come to our attention, we will investigate sources such as film scripts or transcripts of broadcasts if they are available and seem likely to add to our knowledge of the word's origin." Source and further information: http://www.askoxford.com/asktheexperts/faq/aboutdictionaries/choose?view=uk

Usage. Dictionaries report what words are used and how the population uses them. This means that what appears in a dictionary isn't necessarily correct, but only used commonly. New words are added to the dictionary as they become popular.

Some of them hire readers to note the frequency of new word or new meaning use and then decide what goes in and what stays out. They want to avoid printing flash-in-the-pan slang if they can help it but they don't want to be all prissy about language either. 'Awesome' in the slang sense and 'rad' would likely be chosen while 'hella' probably would not.