Speak Selection does not honor selected voice

I have an iPhone X running iOS 11.4.1. I have Speak Selection enabled via the accessibility settings. I have also chosen specific voices for English, French, and Spanish. However, when highlighting text and pressing the 'speak' button, the spoken voice is robotic (presumably Samantha); it is not the voice I selected. Additionally, Speak Selection seems to have difficulty in identifying which language the highlighted text is in. For example, sometimes words in English are spoken in Spanish and vice versa.

I have tried hard rebooting my phone and restoring via iCloud to no avail. Additionally, I encountered the same issue with my iPhone 6S when it was running and earlier version of iOS last Fall.

Also, Speak Screen is seemingly unaffected as it honors my selected voices. However, it is inconvenient to use as I do not want to always have my entire screen of text spoken aloud.

Does anyone have advice on how to fix this bug?

Thanks.