[tex-eplain] ngerman.sty does not work with TeX Live 2015

[Helmut Jarausch]

Hi,

on November, 19th, 2014 I have asked this already (for TeX Live 2014) but either I've got no answer or
I failed to archive the answer.

Therefore, here again

with the file ngerman_test.tex :

\DeclareTextSymbol{\ss}{OT1}{25}
\def\UseTextAccent#1#2#3{%
    {\let\@curr at enc\f at encoding
     \fontencoding{#1}\selectfont
     #2{\fontencoding\@curr at enc\selectfont #3}}}%
\def\ProvideTextCommand#1#2{%
    %%% misses \RobustTextCommand{#1}{...etc.etc...}!!
    \expandafter\providecommand\csname #2\string#1\endcsname}%
\def\ProvideTextCommandDefault#1{%
    \ProvideTextCommand{#1}{U}}%

\ProvideTextCommandDefault{\"}{\UseTextAccent{OT1}{\"}}

\bye

eplain ngerman_test.tex

gives

This is pdfTeX, Version 3.14159265-2.6-1.40.16 (TeX Live 2015) (preloaded format=eplain)
 restricted \write18 enabled.
entering extended mode
(./ngerman_test.tex
Babel <3.9l> and hyphenation patterns for 12 languages loaded.
! Undefined control sequence.
\@startdef ->\expandafter \def \@commandname 
                                             
\@newcommand ...expandafter \@startdef \@paramdef 
                                                  {#1}
\reserved at c ->\@newcommand \U\" 
                                [0]
<to be read again> 
                   {
l.12 \ProvideTextCommandDefault{\"}{
                                    \UseTextAccent{OT1}{\"}}




Is there any solution of work around?
I'm using eplain-3.7

Many thanks for a hint,
and sorry if I failed to archive the answer,

Helmut