The reason some fields are not functioning right is on each step when validation is enabled I am faking a registration submit. This triggers CBs validation and will error any fields that fail validation. This then allows me to stop users from moving to the next step based on the errors presented.

The problem is those special fields have validation beyond just being Required so I need to do something else to remove the validation for them; perhaps disable them or remove them entirely then restore them after validation check. At any rate issue is noted and will be addressing with next release. For the time being keep those fields on the first Step.

1. When I am using the CB Captcha, then it shows the captcha image and input field in every step on top of the form. The field label shows below the form. None of the could be moved no matter what I have tried.

Please test with CB 1.4 if not installed already and ensure are using the latest Captcha. It should only be shown once in its own step.

2. Where do I have to put the language strings to rename the labels for the steps.

CB team plugins language file. You can also define them as defines in the main language file.

2. However, there is still the issue regarding certain fields assigned to certain tabs. For example: I have 2 tabs, portrait and contact. When I assign the username field to the portrait tab, step-by-step works. The field shows up in the first tab of the registration page and I can click to the next tabs.
When I assign the username field to the contact tab, the field does not show up on the first tab (which is correct), but when I try to get to the next tab, the validation message pops up telling me to fill out username. Of course I cannot do this, because the username field has been assigned to the second tab which I cannot select.
Only turning validation off solves this for now as this is the only way to switch to the second tab.
It is weird, that this behaviour does not show for all fields. I have experienced this for the username field, the password field and a customs field of mine. Other fields can be assigned anywhere without showing this weird behaviour.

Am investigating this issue and can not duplicate. With validation on and all core fields such as password, email, name, username, etc.. placed on Step 2 after completing Step 1 I was able to move to Step 2 successfully. Don't believe there is an issue present, please ensure you're using latest release. Please also state if you're using custom validation such as through REGEX or something of the sort. Please also ensure you're using CB 1.4.