Here, I use \stackinset to achieve the goal (stackengine package)
I provide \scaledinset in response to the OP's comment. Thus, rather than #2 and #4 being physical x and y distances, they represent a fraction of the overall width and height of the graphical object.
I also use a standard graphic, rather than an svg, for this demonstration.
\documentclass[standard]{letter}
\usepackage{svg}
\usepackage[usestackEOL]{stackengine}
\usepackage{graphicx}
\newcommand\scaledinset[6]{%
\setbox0=\hbox{#6}%
\stackinset{#1}{#2\wd0}{#3}{#4\ht0}{#5}{#6}
}
\begin{document}
\scaledinset{l}{.5}{b}{.7}{test}{\includegraphics[width=0.15\linewidth]{example-image}}
\scaledinset{l}{.5}{b}{.7}{test}{\includegraphics[width=0.45\linewidth]{example-image}}
\end{document}

\stackinsetof thestackenginepackage. – Steven B. Segletes Sep 10 '19 at 11:47\stackinset{l}{20pt}{b}{20pt}{test}{% \includesvg[width=0.15\linewidth, svgpath=images/]{test-svg} }The only thing is that relative placements (relative to the image size) are not possible as far as I understood the documentation. So I have to adjust the text every time I change the scaling. Do you wanna add your anser as an Answer @Steven – ro-bb Sep 10 '19 at 12:29.pdf_texfile, thesvgpackage can do that for you. Though you would of course have to edit the.svgfile (or the generated.pdf_texfile) in order to change the text. (I don't really see how having to find the correct coordinates by hand and having to change them every time the scaling of the image is changed is less hassle than just placing the text in the.svgfile, which has to be created (i.e. edited) at some point, anyway.) – schtandard Sep 10 '19 at 13:21.pdf_texfiles manually. – ro-bb Sep 10 '19 at 13:33