I recommend using translation chunks as described there:
https://sap.github.io/spartacus-docs/i18n/#configuring-chunks-and-namespace-mapping
Working solution.
In app.module.ts in providers provide this config:
provideConfig({
i18n: {
backend: {
loadPath: 'assets/i18n-assets/{{lng}}/{{ns}}.json',
},
chunks: {
'forms': ['updatePasswordForm'],
},
},
}),
Afterwards, we can create a json file in src/assets/i18n-assets/en/forms.json and inside this file add the following lines:
{
"updatePasswordForm": {
"oldPassword": {
"placeholder": "Old password"
}
}
}
Explanation
loadPath defines the place where the translation chunks will be located.
{{lng}} defines a folder for translations language, e.g., en, de etc.
{{ns}} is placeholder for chunks.
In chunks we defined 'forms' field which corresponds to our translations file - forms.json.
Also, we have to map translations to namespaces - we have defined that our forms.json file contains namespaces ['updatePasswordForm'], so when translations will be needed for namespaces that starts with updatePasswordForm, the forms.json file will be loaded.