I18nize Scala programs à la gettext

i18nize Scala programs
à la gettext
Episode 39, Wed, Aug 12, 2015
Ngoc Dao

About the speaker
● Ngoc Dao
● Joined Atlassian since May

● Favorite languages:
Ruby, Erlang, Scala

● Favorite languages:
Ruby, Erlang, Scala
● My Scala style:
Using Scala as if
Scala =
Java (performance, libs eco) +
Ruby (human oriented) +
Erlang (functional)

● Don’t know Scalaz/Haskell (yet)
↑↑↑
Struggling with
monadic talks at ScalaSyd

English is not my native language
● From Viet Nam
● 15 years in Japan
↑↑↑
i18n is important to me

Given this program:
printf("My name is %s.", myName)

Given this program:
printf("My name is %s.", myName)
Let’s i18nize it in gettext style!
(I won’t go into details of .properties style vs gettext style)

(1) Mark the strings we want to translate
printf(t("My name is %s."), myName)

i18n.pot template file:
msgid "My name is %s."
msgstr ""
(2) Extract to a template file

i18n.pot template file:
msgstr ""
fr.po language file:
msgstr "Je m'appelle %s."
(2) Extract to a template file
(3) Give it to translators

When strings in the program change, how to
update (add, remove, modify) language files
efficiently?

efficiently?
● Automatically copy similar existing
translation to make new translation (marked
as “fuzzy” to be modified by a human later)

efficiently?
● Don’t delete, just comment out dated
translations for future references

efficiently?
● Don’t delete, just comment out dated
translations for future references
● In translation files, sort by msgid so that it’s
easier to diff versions

msgstr "Je m'appelle %s."
ja.po language file:
msgstr "%sと申します。"
(4) Load language files to program,
basically parse the files to
key → value
data structure
vi.po language file:
msgstr "Tôi tên là %s."

printf("Je m’appelle %s.", myName)
(5) At run time, the marker acts as a
function to replace the given key
with its value

gettext is quite advanced
● Allow specifying context
(one string may be translated to
different strings, depending on
context)

print(t("Hello"))
print(tc("Casual", "Hello"))
msgid "Hello"
msgstr "Bonjour"
msgctxt "Casual"
msgid "Hello"
msgstr "Salut"

gettext is quite advanced
● Allow specifying singular/plural rules
(different languages may have
different singular/plural rules)

print(tn(
"I have one apple",
"I have %d apples",
numApples
))
Singular
Plural
Depending on this value

msgid ""
msgstr "Plural-Forms: nplurals=2; plural=n>1;"
msgid "I have one apple"
msgid_plural "I have %d apples"
msgstr[0] "J'ai une pomme"
msgstr[1] "J'ai %d pommes"
Singular/plural rule
Special key

Demo
I’ll introduce some tools

Hello.scala
println("Hello world")

Mark and extract i18n strings
Tool:
https://github.com/xitrum-framework/scala-xgettext
It’s a Scala compiler plugin, to extract i18n
strings at compile time.

Tool:
https://github.com/xitrum-framework/scala-xgettext
It’s a Scala compiler plugin, to extract i18n
strings at compile time.
↑↑↑
Neat! Just compile Scala source code and get the strings.
Scala is powerful

● scala-xgettext can also extracts i18n strings
from view templates
● as long as the templates are converted to
Scala source code and compiled

● scala-xgettext can also extracts i18n strings
from view templates
● as long as the templates are converted to
Scala source code and compiled
↑↑↑
It works for all popular Scala template engines like Scalate,
Scalatags, Twirl (Play framework template engine)

Translate language template file

Tool:
Any text editor

Tool:
Any text editor
Very convenient GUI editor:
https://poedit.net/

Load language file
Tool:
https://github.com/xitrum-framework/scaposer
It’s a Scala parser to transform .po text file into
key → value
data structure

Poedit demo: Update i18n strings
● Add, modify, remove i18n strings in program
● Regenerate i18n.pot file
● Use Poedit to update existing .po files with
the new i18n.pot file
● Poedit can give translation hints for similar
strings

Demo source code:
https://github.com/xitrum-framework/scala-xgettext-presentation
If you use Play framework:
https://github.com/georgeOsdDev/play-xgettext

I18nize Scala programs à la gettext

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