In English, ll often represents the same sound as single l: /l/. The doubling is used to indicate that the preceding vowel is (historically) short, or that the "l" sound is to be extended longer than a single "l" would provide (etymologically, in latinisms coming from a gemination). It is worth noting that different English language traditions transpose "l" and "ll": British English "travelled" and like words, for example, are usually spelled with a single "l" (i.e., "traveled," et al.) in U.S. English.ll
In Welsh, ll stands for a voiceless alveolar lateral fricative sound. The IPA signifies this sound as [ɬ]. This sound is very common in place names in Wales because it occurs in the word Llan, for example, Llanelli, where the ll appears twice, or Llanfairpwllgwyngyll, where the ll appears three times.
In Welsh, 'Ll' is a separate letter from L (e.g. lwc sorts before llaw). This led to its ligature being included in the Latin Extended Additional Unicode block. The capital ligature appears similar to a joined "IL" and the minuscule ligature like "ll" joined across the top. This ligatured character is not used in Modern Welsh.
In Spanish, ll was considered a digraph from 1754 to 2010 as the fourteenth letter of the Spanish alphabet because of its representation of a palatal lateral articulation consonant phoneme (as defined by the Royal Academy of the Spanish Language).
In Catalan, ll represents the phoneme /ʎ/. For example, as in llengua "language" or "tongue", enllaç "linkage", "connection" or coltell "knife". In order to not confuse ll /ʎ/ with a geminated l /ll/, the ligature ŀl is used with the second meaning. For example, exceŀlent is the Catalan word for "excellent", from Latin excellente. In Catalan, l·l must occupy two spaces, so the interpunct is placed in the narrow space between the two L: ĿL and ŀl. However, it is more common to write L·L and l·l, occupying three spaces; this practice is not correct although it is tolerated. L.L and l.l are incorrect and not accepted. See interpunct for more information.
While Philippine languages like Tagalog and Ilokano write ly or li in the spelling of Spanish loanwords, ll still survives in proper nouns. However, the pronunciation of ll is simply [lj] rather than [ʎ]. Hence the surnames Llamzon, Llamas, Padilla and Villanueva are respectively pronounced [ljɐmˈzon]/[ljɐmˈson], [ˈljɐmas], [pɐˈdɪːlja] and [ˌbɪːljanuˈwɛːba]/[ˌvɪːljanuˈwɛːva].
In Icelandic, the "ll" represents either the sound combination [tɬ] (similar to a voiceless alveolar lateral affricate) or [tl], depending on the context. It occurs in the words "fell" (fell, small mountain), "fjall" (mountain), and "jökull" (glacier, ice cap), and consequently in the names of many geographical features, including Eyjafjallajökull.