Child theme does not inherit translations from parent theme

[rossmc]

Summary of the issue
Theme inheritance does not work as expected with translation dictionaries. The child theme does not use any translations defined in it's parent theme's en_US.csv translation dictionary.

Preconditions
I'm working on a Magento ver 2.2.5 installation with two websites & two corresponding theme's. Each with their own translation dictionary, and one theme inheriting from the other.

Steps to reproduce

1. Set up a magento instance with two websites and with two theme's, one inheriting from luma and the other inheriting from the other theme you created. See theme structure below.
2. Add a the translation string "Create New Customer Account","Create New Account" to the parent theme's en_US.csv translation dictionary.
3. Go to the /customer/account/create/ URL for the website with the child theme applied.

Expected result
The page title should be Create New Account

Actual result
The page title is still Create New Customer Account

• If go to the /customer/account/create/ URL for the website with the parent theme applied, the page title should is Create New Account. So the child theme is not picking up translations from the parent theme.
• If you add the translation string "Create New Customer Account","Create New Account" to the Child theme's en_US.csv translation dictionary you can see the translation string applied corectly on the website with the child theme applied.

Is this a bug with Magento or am I doing something wrong?

Is the translation dictionary documentation incorrect and this is actually the correct behaviour?

---

Theme Structure

app/design/frontend/Ross
│
├── parent
│   ├── composer.json
│   ├── i18n
│   │   └── en_US.csv
│   ├── registration.php
│   └── theme.xml
│   
└──  child
    ├── composer.json
    ├── i18n
    │   └── en_US.csv
    ├── registration.php
    └── theme.xml

Parent's theme.xml

<theme xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Config/etc/theme.xsd">
    <title>Ross Parent</title>
    <parent>Magento/luma</parent>
</theme>

Child's theme.xml

<theme xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Config/etc/theme.xsd">
    <title>Ross Child</title>
    <parent>Ross/parent</parent>
</theme>

[magento-engcom-team]

Hi @rossmc. Thank you for your report.
To help us process this issue please make sure that you provided the following information:

• Summary of the issue
• Information on your environment
• Steps to reproduce
• Expected and actual results

Please make sure that the issue is reproducible on the vanilla Magento instance following Steps to reproduce. To deploy vanilla Magento instance on our environment, please, add a comment to the issue:

@magento-engcom-team give me {$VERSION} instance

where {$VERSION} is version tags (starting from 2.2.0+) or develop branches (2.2-develop +).
For more details, please, review the Magento Contributor Assistant documentation.

@rossmc do you confirm that you was able to reproduce the issue on vanilla Magento instance following steps to reproduce?

• yes
• no

@rossmc, thank you for your report.
We've acknowledged the issue and added to our backlog.