E-Mail subject not showing "ü" german Umlaute

[KM-HM]

Preconditions

1. Magento Version 2.2.4 installed via composer
2. PHP 7.0.30-0ubuntu0.16.04.1
   (3. My magento has this module https://github.com/magepal/magento2-gmail-smtp-app)

Steps to reproduce

1. Create a e-mail template containing a "ü" (üäö german stuff) in the subject
2. Create an Order to get the E-mail
3. View the email in outlook (web.de was also reported to me)

Expected result

1. E-mail subject should display the "ü" like it was authored

Actual result

1. E-mail subject shows "?" question mark in the same position as the "ü" should be

I resolved this issue by creating a plugin for Magento\Email\Model\Template method getSubject/afterGetSubject with utf8_encode($result) to UTF-8 encode the result.
This seems to be working for now.

Note for the module mentioned in the preconditions:
https://github.com/magepal/magento2-gmail-smtp-app
This module was installed before I upgraded to Magento 2.2.4 from 2.1 and there were no issues with the encoding of the subject line

Also the System does not retrieve the subject line when opening the email template.

[ymarc77]

I noticed this same problem… Any diacritics in the subject line is converted to "?".

[KM-HM]

@ymarc77 Tell as your Magento version please

[ymarc77]

Magento 2.2.4, noticed on 2.2.3 too.

[KM-HM]

Did you recently Upgrade to 2.2.X ?

The Magento instance I'm working on was only affected when I upgraded to 2.2.4 from 2.1.x

[ymarc77]

No. I migrated from 1.8.1 to 2.2.1, then updated to 2.2.2 and 2.2.3.

[kkrieger85]

#mhlej18