Your file `/app/i18n/test/xx_YY/dictionary.csv` should be have four columns 


 1. The value of Translate
 2. The value should be translated with this.
 3. Module used simply `module`
 4. Module Name of that particular translator e.g. `Magento_Catalog`


**e.g**

**`Save Category`	`Save Category New `   	`module`	`Magento_Catalog`**


**AND**

    [InvalidArgumentException] Specified path doesn't exist
for this, you have to collect translate variable from Magento2 Root

**use**

`php bin/magento i18n:collect-phrases -o "/app/i18n/test/xx_YY/dictionary.csv" Magento2ROOT/`


**instead of**

`php bin/magento i18n:collect-phrases -o "/app/i18n/test/xx_YY/dictionary.csv" /vendor/magento`



it will help you.