Umbrello use in the main toolbar icons and text but in the diagramm toolbar there are only icons. As there are only very specific icons in the diagramm toolbar I would suggest du add there the text in the standard settings too. In addition in the main toolbar there is no text for print and preview. Reproducible: Always
> In addition in the main toolbar there is no text for print and preview. I can confirm in the toolbar "text position" mode "text beside symbol" As addition redo/undo buttons also do not show any text in the toolbar "text position" mode "text beside symbol" > in the diagramm toolbar there are only icons. This requires to set the initial state of the diagram toolbar text position to "text beside symbol"
umbrello uses a method from the KDE gui library (KStandardAction::printPreview()) to create the common actions like new, print, print preview menu entries. These actions are also used for the toolbar. In KDE4 builds the text is missing in "text beside icon" mode for new, print, print preview, undo and redo. In KF5 builds the texts for new, undo and redo are shown, but still not displayed for print and print preview, which looks really like an issue in some of the base libraries.
That the text is not shown for some icons in 'Text Alongside Icons' mode caused by a toolbar item settings. To change the visiblity of an icon text: 1. right-click on toolbar 2. select "configure Toolbar" 3. select related action and press "change Text" 4. select or deselect "Hide text when toolbar shows text alongside icons