Removes UTF.8 local warnings

Entire-Checkpoint: 01M2ATPS2NW3GTF98PWMWFZJ0Y

app/Dockerfile

@@ -55,10 +55,13 @@ RUN apt-get update \
         libkf6texttemplate-dev \
         qt6-tools-dev-tools \
         qt6-tools-dev \
+        locales \
         unzip \
         python3 \
         python3-venv \
         python3-pip \
+    && locale-gen en_US.UTF-8 C.UTF-8 \
+    && update-locale LANG=C.UTF-8 LC_ALL=C.UTF-8 \
     && ln -sf /usr/bin/python3 /usr/local/bin/python3 \
     && ln -sf /usr/bin/python3 /usr/local/bin/python \
     && rm -rf /var/lib/apt/lists/*