A Pseudolocalization tool for Flutter which generates pseudo, nonsensical translations for multiple languages from a given English source.


  • Internationalization is the process of designing a software application so that it can easily be adapted to various other languages and regions without any programming changes.
  • Localization is the process of adapting internationalized software for a specific region or language by adding locale-specific components (€2.99 => 2,99€) and translating text (Hello World! => Hallo Welt!).
  • Pseudolocalization is a software testing method used before the localization process in which a fake (or pseudo) translations (with the region and language specific characters) are generated: Hello World! => [ Hellö Wörld! ÜüäßÖ ].

The benefits of pseudolocalization are three fold:

  1. To test that all (special) characters of the target locale (i.e. German) are displayed correctly.
  2. To test that text boxes can accommodate longer translations. If a pseduotranslation is cutoff or visually looks ugly on the screen, then there's a good chance that the real translation will too.
  3. To flag hardcoded strings or text images.

Character Replacement

Generally psuedo translations will replace characters in the English string (i.e. Hello World) with special (i.e. accented) characters from the target language. Considering German, the special characters ä ö ü ß Ä Ö Ü ẞ could be mapped to vowels a, o and u, with ß mapped to b. Although the letter ß has no relationship to b in German, what is important here is that the text is as readable as possible for the developer. The pseudo translation may also use a mixture of all UTF-8 special characters.

Text Expansion

Considering English as the base language, after translation many languages will exhibit text expansion and have longer text strings. Generally German extends by 10-35%, Polish 20-30% and Russian by 15%. Moreover, shorter English text strings tends to expanded even more than larger strings. Thus one approach to text expansion is to use a constant (say 40%), while another is to use a function of input text length returning values from 30-50%. Note that some languages (i.e. Japanese, Korean) generally contract and can actually have shorter text strings than their English counterparts.

Text Expansion Format

There are multiple ways to format the text expansion, for instance:

  • appending random special characters: Hellö Wörld äßÜẞ.
  • repeating all vowels multiple times: Heellöö Wöörld.
  • appending number words: Hellö Wörld one two.
  • wrapping the base text with exclamation marks: !!! Hellö Wörld !!!)

Moreover, the text expansion is often wrapped in square brackets to easily determine UI clipping, while it may also use punctuation of the target language (i.e. ¿ and ¡ in Spanish).

Pseudo Translations

Putting this altogether, the base string can be rendered as follows:

English Hello World!
German Hellö Wörld! ÜüäßÖ
Polish Hęęęłłóóó Wóórłd!
Russian !!! Нёлло Шоялд! !!!
Spanish Hélló Wórld! one two

It is important to remember that these pseduotranslations are nonsensical: they are not real translations, instead merely a way to test that the app is ready for the translation stage.

Getting Started

Firstly, add the package as a dev dependency:


Next define settings in pubspec.yaml for the package:

  input_filepath: "test.arb"
  replace_base: true
    - latinSupplement
    - latinExtendedA
  use_brackets: true
  text_expansion_format: 'repeatVowels'
  text_expansion_ratio: null
    - de
    - pl
    - ru
    - '%(\S*?)\$[ds]'
    - 'Flutter'
    - 'title'
    output_directory: 'l10n_pseudo'
    output_filepath: 'test_PSEUDO.csv'
    delimiter: ";"
    column_index: 1
Setting Description
input_filepath A path to the input localization file.
replace_base Whether the base language (en) should be replaced. Defaults to false.
unicode_blocks When replace_base is true, a list of unicode blocks to use. Defaults to all.
text_expansion_format The format of the text expansion. Defaults to repeatVowels, alternatives append, numberWords, exclamationMarks.
text_expansion_ratio The ratio (between 1 and 3) of text expansion. If null, uses a linear function.
languages_to_generate A list of languages to generate. Defaults to empty.
patterns_to_ignore A list of patterns to ignore during text replacement.
keys_to_ignore A list of keys which should be ignored.
arb_settings Optional settings when the input file is an arb, please see below for more info.
csv_settings Optional settings when the input file is a csv file, please see below for more info.

input_filepath must be given, all other settings are optional.

replace_base replaces the base language (en) with characters from unicode_blocks. To test specific languages, set languages_to_generate with a list of languages. patterns_to_ignore is especially useful to avoid text replacement for certain know constructs, for instance a product name or a pattern %myVar$d used to parse variables from text.

ARB Setting Description
output_directory An optional directory for generated files. Defaults to l10n_pseudo.
CSV Setting Description
output_filepath A path for the generated output file. Defaults to <input_filename>_PSEUDO.csv.
delimiter A delimiter to separate columns in the input CSV file. Defaults to ,.
column_index The column index of the base language (en) in the input CSV file. Defaults to 1.

Ensure that your current working directory is the project root, then run the terminal command:

dart run flutter_pseudolocalizor


flutter pub run flutter_pseudolocalizor

to generate output files.

Future Plans

  • Presently 500 non-basic latin characters are available.
    • IPA Extensions, Phonetic Extensions, Latin Extended Additional, Latin Extended Additional, Letterlike symbols will be considered in future versions.
  • Although 8 languages are currently supported, some of the world's most spoken languages like Arabic, Chinese and Hindi are not supported.
    • For languages with their own alphabets (like Arabic, Armenian, Georgian, Hindi, Korean etc.), one approach could be to append random letters from the alphabet onto the original English text.
    • For character based writing systems like Chinese, Japanese etc., maybe random characters could be appended to the original English text.
  • If the Russian mapping is positively received, other languages which use the Cyrillic alphabet and Greek could be similarly implemented.
  • Migrate to use Characters class over Strings.


Spotted any issues? Please open an issue on GitHub! Would like to contribute a new language or feature? Fork the repo and submit a PR!