The main examples of infixes in the world's languages are in the
Austric group, which is a hypothetical superfamily centred around
South-East Asia, including both the
Mon-Khmer languages (such as
Khmer or Cambodian) and the
Austronesian languages (such as
Indonesian and those of the Philippines and Polynesia). In fact the sharing of infixes is one reason some linguists suspect the families are related.
In Khmer, charoen means 'causing prosperity' and chamroen means 'to prosper'. (The infix is actually -am-.) This has been borrowed into Thai, which does not belong to either family, and both words mean 'prosper'. Pak means 'rest' in Thai, pnak means '(physical) support', and pamnak means 'mental or moral support'. These are not isolated examples: the process is highly productive in these languages.
In Sora, a member of the Munda family, an Indian branch related to Mon-Khmer, some elements are prefixes before a vowel and infixes after a consonant. So id 'scratch' forms Arid 'scratching tool', whereas pO 'pierce' forms pArO 'piercing tool'. (A and O represent vowels different from a, o.) Interestingly, there is another prefix Ar- which stays a prefix: Arid 'scratch each other', ArpO 'pierce each other'.
There are traces of a nasal infix in the present tense of some Indo-European verbs. In English stand vs stood is the only relic of this, but it is more common in Latin (tango 'I touch', tetigi 'I touched', tactum 'touched') and in Greek (lambano 'I take', elabon 'I took').
Infixation is a process of adding material into an existing stem. The term is not usually used for changes within a stem such as the ablaut of sing ~ sang ~ sung, nor of the pattern morphology of Semitic languages.
Asian language examples from:
www.linguistlist.org/issues/4/4-888.html
http://ri.xu.org/conlang/conl92c.txt
www.asiatour.com/thailand/e-01land/et-lan51.htm