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.

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.