Compatible LibreOffice Dictionary & Hyphenation Files

LibreOffice relies on open-source linguistic backends to manage spell checking, hyphenation, and thesaurus lookups. To expand or customize language support, users and developers can integrate specific dictionary formats and hyphenation pattern files. This guide details the exact file formats, engines, and packaging standards compatible with LibreOffice.

Spell Checking Dictionaries

LibreOffice primarily uses Hunspell as its default spell-checking engine, while maintaining backward compatibility with MySpell. To function properly, a spell-checking dictionary requires a pair of two files sharing the exact same base name:

• .dic (Dictionary File): Contains the word list along with rule flags assigned to individual words.
• .aff (Affix File): Defines the language rules, such as prefixes, suffixes, compound word rules, character encodings, and replacement suggestions.

Hyphenation Patterns

LibreOffice uses Libhyphen, a hyphenation library based on Franklin Mark Liang’s TeX hyphenation algorithm. Hyphenation rules are defined using standard TeX-derived pattern files:

• hyph_*.dic (Hyphenation Dictionary File): Unlike spelling .dic files, hyphenation .dic files contain numerical hyphenation patterns and rules indicating valid breakpoints in words.
• Encoding Header: These files must specify the character set at the top (e.g., UTF-8 or ISO8859-1) to process special characters and accents accurately.

Thesaurus Files

For synonym and antonym lookups, LibreOffice implements MyThes. Similar to Hunspell, MyThes requires a pair of complementary files:

• .dat (Data File): Contains the indexed words, parts of speech, and lists of synonyms.
• .idx (Index File): Contains byte-offset pointers that allow LibreOffice to rapidly search the .dat file.

Packaging and Integration Formats

While raw files can sometimes be manually placed into LibreOffice’s system folders, the standard and most reliable method for installing language data is through extensions:

• .oxt (OpenOffice / LibreOffice Extension): A zip-compressed archive containing the .aff, .dic, .dat, and .idx files.
• dictionaries.xcu (Configuration XML): Included inside the .oxt package to register which language codes (BCP 47 / ISO 639-1) map to the corresponding spell check, hyphenation, or thesaurus files.
• description.xml: Contains the metadata, extension version, and LibreOffice minimum version requirements.