@timwhitlock I double checked. In my Child theme there’s no need for system or author. As long as I have the translations in custom folder it’s working.
This is the beginning my child theme xxx-ja.po file:
msgid ""
msgstr ""
"Project-Id-Version: Hello Elementor Child IIC\n"
"Report-Msgid-Bugs-To: \n"
"POT-Creation-Date: 2021-11-08 14:50+0000\n"
"PO-Revision-Date: 2024-11-14 10:29+0000\n"
"Last-Translator: \n"
"Language-Team: Japanese\n"
"Language: ja\n"
"Plural-Forms: nplurals=1; plural=0;\n"
"MIME-Version: 1.0\n"
"Content-Type: text/plain; charset=UTF-8\n"
"Content-Transfer-Encoding: 8bit\n"
"X-Generator: Loco https://localise.biz/\n"
"X-Loco-Version: 2.6.6; wp-6.7\n"
"X-Domain: iic_corsi"
#: includes/inc-woocommerce.php:900
msgid "%d Place Still Available"
msgid_plural "%d Places Still Available"
msgstr[0] "残席%d名"
#: includes/inc-shortcodes.php:821
#, php-format
msgid "%s Available classes"
msgstr "開講クラス数:%s"
#: includes/inc-shortcodes.php:814
#, php-format
msgid "%s Class Available"
msgstr "開講クラス数:%s"
Parent theme has translations only in the default “system” folder (never touched or used it).
this is the beginning of my hello-elementor-ja.po
# Translation of Themes - Hello Elementor in Japanese
# This file is distributed under the same license as the Themes - Hello Elementor package.
msgid ""
msgstr ""
"PO-Revision-Date: 2024-06-21 13:43:06+0000\n"
"MIME-Version: 1.0\n"
"Content-Type: text/plain; charset=UTF-8\n"
"Content-Transfer-Encoding: 8bit\n"
"Plural-Forms: nplurals=1; plural=0;\n"
"X-Generator: GlotPress/4.0.1\n"
"Language: ja_JP\n"
"Project-Id-Version: Themes - Hello Elementor\n"
#. Description of the theme
#: style.css
#, gp-priority: high
msgid "Hello Elementor is a lightweight and minimalist WordPress theme that was built specifically to work seamlessly with the Elementor site builder plugin. The theme is free, open-source, and designed for users who want a flexible, easy-to-use, and customizable website. The theme, which is optimized for performance, provides a solid foundation for users to build their own unique designs using the Elementor drag-and-drop site builder. Its simplicity and flexibility make it a great choice for both beginners and experienced Web Creators."
msgstr "Hello Elementor は、Elementor サイトビルダープラグインとシームレスに動作するように特別に構築された、軽量でミニマルな WordPress テーマです。このテーマは無料のオープンソースで、柔軟で使いやすく、カスタマイズ可能なサイトを求めるユーザー向けに設計されています。パフォーマンスが最適化されたテーマは、Elementor のドラッグアンドドロップサイトビルダーを使用してユーザーが独自のデザインを構築するための強固な基盤を提供します。そのシンプルさと柔軟性により、初心者にも経験豊富な Web クリエイターにも最適です。"
#. Theme Name of the theme
#: style.css
#, gp-priority: high
msgid "Hello Elementor"
msgstr "Hello Elementor"
#: includes/settings/settings-footer.php:600
#: includes/settings/settings-header.php:634
msgid "Elementor Pro"
msgstr "Elementor Pro"
Hope it helps