That world languages contain words with consecutive repeating syllables is a straightforward linguistic fact, widely observable in phenomena like reduplication and child-directed speech across human languages, and requires no formal citation.
The claim asserts that world languages exist in which consecutive syllables repeat within words. This is a basic, universally recognized linguistic fact (exemplified by reduplication processes, baby talk, and lexical items in languages like Malay, Tagalog, and many others). Per Step 0 of the prompt instructions, a claim that is trivially true by direct everyday observation or basic definition is classified as COMMON_KNOWLEDGE. No citation is needed, and paper indices are left empty.